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NETAPP

VTL

NetApp VTL Operations Guide with BestPractices

Version 1.0

NetApp, Inc.

495 East Java DriveSunnyvale, CA 94089 U.S.A.Telephone: +1 (408) 822-6000Fax: +1 (408) 822-4501Support telephone: +1 (888) 4-NETAPPDocumentation comments: [email protected] Web: http://www.netapp.com

Part number: 215-04472_A0March 5, 2009
mailto:[email protected]:[email protected]


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Copyright and Trademark Information

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Table of Contents

1 INTRODUCTION.......................................................................................................................................................72 ACCESS TO THE NOW SITE...................................................................................................................................83 NETAPP VTL ARCHITECTURAL OVERVIEW........................................................................................................93.1 Introduction to NetApp VTL................................................................................................................................93.1.1 Backup Workflow ............................................................................................................................................123.2 Hardware Overview ...........................................................................................................................................133.3 NetApp VTL Deduplication (VTL 6.0 and Later) ........... .......... .......... ........... .......... ........... .......... .......... ........... 163.3.1 Requirements for Effective Deduplication .......................................................................................................173.3.2 What is Different in VTL 6.0 ............................................................................................................................193.3.3 Deduplication Configuration and Monitoring GUI Overview ............................................................................193.3.4 VTL 6.0 Workflow Example.............................................................................................................................213.3.5 VTL Duty Cycles .............................................................................................................................................224 GENERAL BEST PRACTICE RECOMMENDATIONS...........................................................................................244.1 NetApp VTL Compatibility List.........................................................................................................................244.2 AutoSupport ......................................................................................................................................................244.3 VTL Serial Console............................................................................................................................................244.4 When to Reboot a VTL ......................................................................................................................................244.5 Backup Application Multiplexing.....................................................................................................................254.6 Stream Count Recommendations....................................................................................................................264.6.1 VTL Releases Prior to 5.5 ...............................................................................................................................264.6.2 VTL 5.5 and 5.6...............................................................................................................................................264.6.3 VTL 6.0 ...........................................................................................................................................................264.7 Virtual Tape Drive Unload/Unmount Policy for VTL 6.0 .......... .......... ........... .......... .......... ........... .......... ......... 274.8 Tivoli Storage Manager.....................................................................................................................................274.8.1 General Considerations ..................................................................................................................................284.8.2 Virtual Library Configuration............................................................................................................................284.8.3 Tivoli Storage Manager Mount Retention Settings ..........................................................................................294.9 Physical Library Sharing ..................................................................................................................................294.10 Number of Initiators per VTL Port....................................................................................................................294.11 Virtual Tape Record Size ..................................................................................................................................304.12 Enable VTL HTTP and SSH Ports.....................................................................................................................305 VTL MONITORING .................................................................................................................................................315.1 Administrator Overview....................................................................................................................................315.2 Actions Required...............................................................................................................................................315.3 Notifications.......................................................................................................................................................315.4 Statistics ............................................................................................................................................................325.4.1 Virtual Library I/O Load ...................................................................................................................................335.4.2 RAID Group I/O Load......................................................................................................................................335.4.3 Physical Tape Device I/O Load.......................................................................................................................345.5 Import/Export Requests....................................................................................................................................345.6 Event Log...........................................................................................................................................................345.7 Deduplication Tasks (VTL 6.0) .........................................................................................................................345.7.1 Background Tasks ..........................................................................................................................................345.7.2 Postprocessing Window..................................................................................................................................345.7.3 Deduplication Status .......................................................................................................................................355.7.4 Task Management ..........................................................................................................................................355.7.5 Deduplication Task Scheduling.......................................................................................................................365.8 Capacity Management.......................................................................................................................................365.8.1 VTL 5.5/5.6 without DTC or Overallocation.....................................................................................................365.8.2 VTL 5.5/5.6 with DTC and/or Overallocation...................................................................................................375.8.3 Sizing the VTL to Avoid Running out of Disk Space........................................................................................385.8.4 VTL 6.0 ...........................................................................................................................................................385.9 VTL Maintenance Procedures..........................................................................................................................425.9.1 Configuration Management.............................................................................................................................425.9.2 VTL Software Updates ....................................................................................................................................425.9.3 Disk Drive Replacement..................................................................................................................................425.9.4 VTL Troubleshooting.......................................................................................................................................426 PHYSICAL TAPE MANAGEMENT OPERATIONS................................................................................................436.1 Direct Tape Creation (DTC)...............................................................................................................................436.2 Physical Tape Caveats and Best Practices.....................................................................................................446.3 Shadow Tape Caveats and Best Practices......................................................................................................44

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6.3.1 VTL 6.0 and Shadow Tapes............................................................................................................................456.4 Cloning a Virtual Tape to a Physical Tape ......................................................................................................456.4.1 Deferred Cloning.............................................................................................................................................466.4.2 VTL 6.0 Specific Behavior...............................................................................................................................466.5 Exporting from a Virtual Library to a Physical Library...................................................................................466.5.1 VTL 6.0 Specific Behavior...............................................................................................................................466.6 Tape Drive Cleaning..........................................................................................................................................476.7 Physical Tape Drives Maintenance Operations........... .......... .......... ........... .......... ........... .......... .......... ........... 477 RESTORE...............................................................................................................................................................487.1 Restore Operation with Tapes in the Virtual Library......................................................................................487.2 Restore Operation with Tapes not in the Virtual Library .......... .......... .......... ........... .......... ........... .......... ....... 487.3 Manually Importing Tapes into a VTL Caveats and Best Practices ........... .......... ........... .......... ........... ...... 527.3.1 Manually Importing Shadow Tapes .................................................................................................................527.3.2 Manually Importing Physical Tapes.................................................................................................................527.4 Automated Shadow Tape and Physical Tape Import .......... ........... .......... .......... ........... .......... ........... .......... ..547.4.1 VTL Integration Script with NetBackup............................................................................................................548 PHYSICAL TAPE VAULTING AND RECYCLING..................................................................................................558.1 Moving Tapes from the Physical Library.........................................................................................................558.1.1 Opening the Main Door on the Physical Drives...............................................................................................558.1.2 Using the Entry/Exit Port (EEP).......................................................................................................................568.1.3 Offsiting Policies..............................................................................................................................................568.2 Making New or Returning Tapes Available .....................................................................................................578.2.1 Recycling ........................................................................................................................................................578.3

Automating Physical Tape Vaulting and Recycling ........... .......... .......... ........... .......... ........... .......... .......... ....59

9 USING VTL WITH OTHER NETAPP PRODUCTS .................................................................................................609.1 Backup Data on a NetApp FAS system...........................................................................................................609.2 Using VTL with NetApp DataFort .....................................................................................................................6110 APPENDIX A: NETAPP VTL UPGRADE ...............................................................................................................6210.1 VTL OS Upgrade Process.................................................................................................................................6210.2 VTL Shelf Firmware Upgrade Process and Best Practices............................................................................6210.2.1 Shelf Firmware Upgrade Process ...................................................................................................................6210.2.2 Upgrading from VTL Release 5.2.2 or Earlier .................................................................................................6211 APPENDIX B: REFERENCES................................................................................................................................63List of Tables

Table 1 - Tivoli Storage Manager configurations......................................................................................... 28Table 2 - VTL sizing example ...................................................................................................................... 38Table 3 - Reference documents................................................................................................................... 63List of Figures

Figure 1 - NetApp VTL data center ................................................................................................................. 9Figure 2 - NetApp VTL Direct Tape Creation................................................................................................ 11Figure 3 - NetApp VTL backup solution setup example................................................................................ 13Figure 4 - NetApp VTL300 connectivity diagram .......................................................................................... 14Figure 5 - NetApp VTL300 locations diagram............................................................................................... 15Figure 6 - NetApp VTL700 connectivity diagram .......................................................................................... 15Figure 7 - NetApp VTL700 locations diagram............................................................................................... 16Figure 8 - Dedupe ratio ................................................................................................................................. 18Figure 9 - NetApp VTL options...................................................................................................................... 19Figure 10 - Virtual library list ....................................................................................................................... 20Figure 11 - Deduplication tasks .................................................................................................................. 20Figure 12 - Virtual tape list .......................................................................................................................... 21Figure 13 - Dedupe Configuration page ..................................................................................................... 21Figure 14 - Duty cycles in 5.x ..................................................................................................................... 22Figure 15 - Duty cycles in 6.0 ..................................................................................................................... 23Figure 16 - Multiplexing............................................................................................................................... 25Figure 17 - Administrator Overview screen ................................................................................................ 31Figure 18 - Statistics screen ....................................................................................................................... 32



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Figure 19 - Dedupe Configuration screen................................................................................................... 35Figure 20 - Deduplication tasks .................................................................................................................. 35Figure 21 - Dedupe Configuration screen................................................................................................... 36Figure 22 - Compression ratio at appliance level ....................................................................................... 39Figure 23 - Compression ratio at virtual library level .................................................................................. 40Figure 24 - Compression ratio per virtual tape ........................................................................................... 40Figure 25 - Export with shadow tapes ........................................................................................................ 43Figure 26 - Cloning and export ................................................................................................................... 44Figure 27 - Create virtual tapes using the barcodes option........................................................................ 58Figure 28 - Import virtual tapes from physical library with the quick-load option........................................ 59Figure 29 - NDMP Fibre Channel (SAN)-attached model ....................................................................... 60Figure 30 - NetApp DataFort FC525 (2 port) architecture....................................................................... 61



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Preface

NetApp creates innovative storage and data management solutions that accelerate businessbreakthroughs and deliver outstanding cost efficiency. Discover our passion for helping companiesaround the world go further, faster at www.netapp.com.

The purpose of this document is to detail the best practices for everyday VTL management operations;it is not to be used as a configuration guide. The NetApp VTL Troubleshooting Guideis used inconnection with this document. For additional information, see Appendix B - References.

AUDIENCE

The document is primarily intended for NetApp Virtual Tape Library (VTL) administrators.

NON-DISCLOSURE REQUIREMENTS

Copyright 2009 NetApp. All rights reserved. This document contains the confidential and proprietaryinformation of NetApp, Inc. Do not reproduce or distribute without the prior written consent of NetApp.

FEEDBACK

We continually try to improve the quality and usefulness of NetApp documentation. If you have anycorrections, feedbacks, or requests for additional documentation, send an e-mail message to [email protected].

INFORMATION ABOUT THIS DOCUMENT

All information about this document including version history, review and approval, typographicalconventions, references, and a glossary of terms can be found in the final chapter of this document.

http://www.netapp.com/mailto:[email protected]:[email protected]:[email protected]:[email protected]://www.netapp.com/


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1 Introduction

This guide introduces the NetApp VTL appliance and provides configuration and operations information.Its objective is to familiarize VTL administrators with NetApp VTL functionality, operations, and best useof VTL for day-to-day management.

This guide provides information about how to configure and use a NetApp VTL appliance, and enables

administrators to understand and work with virtual libraries and volumes.

This guide is designed for a qualified system administrator. It is assumed that this person is familiar withstorage area network (SAN) and backup applications.



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2 Access to the NOW Site

This document refers to content on the NOW (NetApp on the Web) site. A customer login name andpassword are required to access these links.

To log in to the NOW site, perform the following steps:

Click the following link or paste the link in the URL field of your web browser: http://now.netapp.com

Log in using your user name and password.

http://now.netapp.com/http://now.netapp.com/


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3 NetApp VTL Architectural Overview

NetApp VTL software combines a hardware controller and one or more disk subsystems into a singlesystem that publishes virtual tape libraries on a SAN. These virtual tape libraries are direct, plug-and-play equivalents for physical tape libraries.

3.1 Introduction to NetApp VTL

NetApp VTL appliances operate like physical tape libraries to the backup application (Figure 1).

Figure 1 - NetApp VTL data center

For example, the NetApp VTL retains the native format of the backup application. When the NetAppVTL copies data to the physical tape, the result is a physical tape that is in the native format of thebackup application. The backup application can then restore data from these tapes directly.

The major features of a NetApp VTL appliance are as follows:

Transparency to the backup application: The backup application writes data to the VTL in thenative format and the VTL behaves like a physical tape device. Virtual tape libraries take less time toback up the data.



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Virtual tape libraries: Like their physical counterparts, virtual tape libraries have cartridge slots, oneor more tape drives, an import/export slot, and a robotic arm. These attributes (the number of slots,the capacity of tape drives, and so on) are set when the virtual library is created. NetApp VTL comeswith a number of predefined virtual library types. New library types can also be created to fit theneeds.

Virtual tape drives: The NetApp VTL includes a number of virtual tape drive types. The typespecifies properties such as vendor information, the capacity of the drive, and the tape optimizationalgorithm.

Virtual tapes: Virtual tapes are the NetApp VTL equivalents of physical tapes. Like physical tapes,virtual tapes have a specified capacity and are labeled by barcodes. Backup applications use thesebarcodes to track virtual tapes in the same way that they track physical tapes. There is a one-to-onecorrespondence between the virtual and physical barcodes. The backup application considers virtualtapes as their equivalent physical tapes.

Direct Tape Creation (DTC): The NetApp VTL can export data to physical tapes directly by copyingvirtual tapes to a physical tape library connected to its backend. This feature is also known as DirectTape Creation (DTC). The physical tapes are written in the native format of the backup applicationso that when virtual tapes are exported to physical tapes, there is a 100% match between the two.This implies that any virtual tape that is stored on the NetApp VTL and written to a physical tape canbe restored from any standard tape drive that is supported by the backup server. It is thereforepossible to back up data to the disk while keeping the data offsite on physical tapes that are stored

in the native format of the backup application. Control of physical library Entry/Exit Port (EEP): The correspondence between virtual tape

movement and physical tape movement extends to the movement of tapes, into and out of thelibraries. When moving a virtual tape that has a corresponding physical tape to the virtual libraryentry/exit port, the NetApp VTL can also move the physical tape to the physical library EEP (this iscontrolled by the Move Physical Tapes to EEP after Virtual Export advanced option).

Control of ACSLS-managed libraries: The NetApp VTL appliance can use the physical tapelibraries controlled by Sun/STK Automated Cartridge System Library Software (ACSLS). TheACSLS server and the VTL appliance communicate over a LAN, while the ACS tape drivescommunicate with the NetApp VTL appliance over the SAN. The NetApp VTL appliance does notcommunicate directly with the ACS robotic arms.

In addition to the networking and SAN requirements, you must set the advanced option Use

ACSLS to control the physical libraries, before using an ACSLS with a NetApp VTL appliance.

Note: Either Fiber Channel managed libraries or ACSLS-controlled libraries can be attached to aNetApp VTL appliance, but not both. Before trying to configure the VTL appliance to use an ACSLS-controlled library, ensure that no Fiber Channel managed library is attached to the appliance.

Import/export: When importing a physical tape, the NetApp VTL creates a virtual tape that is anexact copy of the physical tape including the barcode and file mark information. Similarly, whenexporting a virtual tape, the NetApp VTL sends data from the virtual tape to an attached physicaltape device, resulting in a physical copy of the virtual tape.

The cloning feature of the backup application (sometimes called inline copy) can also be used asa slower alternative. The tapes that the NetApp VTL creates are in the native format of the backupapplication.

Each virtual tape has an export status that suggests whether there is a need to copy this tape to aphysical tape. Therefore, the export status is one of the following:

Needs export: a virtual tape that contains data, and is ejected from a virtual tape drive or library.

Does not need export: an empty virtual tape or a virtual tape that is already copied to a physicaltape.

Tape exports are triggered when one of the following occurs:



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The tape is ejected from the virtual library: The backup application ejects a tape from the library,based on its offsite policies (if applicable), and the NetApp VTL recognizes the event (tape moved tothe EEP), locates the corresponding physical tape, and initiates the copy.

The tape export is manually triggered: It is possible to trigger exports by changing the exportstatus of a tape. This is useful to re-create missing or failed physical tapes.

Figure 2 - NetApp VTL Direct Tape Creation

After the tape export, the virtual tape is deleted (unless the shadow tape feature is enabled).

Shadow tape pool and shadow tapes: While exporting a virtual tape, in parallel with the creationof the physical tape, NetApp VTL can create a shadow tape that is stored in the shadow tape pool.The shadow tape pool is a special storage pool inside the VTL; it is not visible from the backupapplication. The backup application continues to manage the physical tape, with the shadow tapeinvisible to the backup application (and invisible to the library on the NetApp VTL). A shadow tapecan be instantly imported back to a virtual library, which makes it immediately available for restores.

Shadow pool is managed in a way that does not affect normal VTL functionality. In case the VTL isrunning short of space, the shadow tape pool is automatically reduced. Shadow tapes are alsoassigned a retention period within a VTL. When a backup application is writing to the NetApp VTL, ifthe NetApp VTL needs additional space for an existing virtual tape, the VTL reclaims the shadow tape

space. Space is reclaimed first from the expired shadow tapes; but if more space is needed even afterreclaiming the expired tapes, it can be reclaimed from the unexpired shadow tapes.

Cloning: VTL cloning is similar to the export process, but with cloning, a copy of the data is alwaysretained on the disk (regardless of whether the shadow tape feature is used). That is, cloning meansexporting the data to the physical tape without deleting the corresponding virtual tape (or withoutmoving the virtual tape to shadow tape).

Smart cloning and tape exporting: When a tape is cloned or exported, and the (virtual) tape isupdated, the NetApp VTL keeps track of the location of change (the point starting from where thephysical tape differs from the virtual tape). When the tape is again cloned or exported, the NetApp



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VTL needs to write data to the physical tape beginning from the location of change. Smart cloning isa default behavior.

Disk compression: While smart sizing adjusts the size of a virtual tape to match the capacity of aphysical tape by taking into account the physical tape drives own data compression algorithm, VTLdata compression reduces the size of the data stored on a virtual tape, which in turn, saves diskcapacity. NetApp VTL appliances support hardware-based disk compression. Hardware-basedcompression has high speed and is a recommended procedure. Data compression can beseparately enabled or disabled for each virtual tape (the default, data compression on or off, can be

set separately for each virtual library when the library is created).

When compression is enabled, the NetApp VTL appliance selects hardware compression, or itselects software compression if hardware compression is not available. For both hardware-basedand software-based compression, the compression ratio depends on the actual data compressed.

Note: VTL 6.0 also supports data deduplication. For details, see section 3.3 NetApp VTL Deduplication(VTL 6.0 and Later).

Smart sizing: This feature is aimed at maximizing the storage efficiency of the physical tapes thatare managed by the VTL. All data is compressible at different rates. This implies that the actualamount of data that the physical tape drive writes to the tape depends on the compressibility of thedata. It is crucial that the amount of data on the virtual tape fits on the physical tape, without goingover its capacity, because the NetApp VTL must be able to export virtual tapes to physical tapes. If

the data from a virtual tape cannot fit on a physical tape, it cannot be exported or cloned.Most VTL vendors solve this issue by matching the capacity of virtual tapes to the native(uncompressed) capacity of the corresponding physical tapes. This is not an efficient solution becauseit does not take compression into account. For example, if the physical tape drive can compress dataat a ratio of 2:1, more than half of the physical tape remains unused when the virtual tape is exported.With smart sizing, the data stream is monitored to determine the compressibility of the data. Thisallows the VTL to determine the appropriate size to fit the virtual tape to the corresponding physicaltape. There is no performance impact when using smart sizing.

Note that smart sizing is completely different from disk compression. Smart sizing optimizes theutilization of physical tape media, while disk compression minimizes the space used on the disk by theVTL. With hardware compression, this is an extremely effective method of saving space on the disk.Smart sizing and disk compression can be used at the same time on the same NetApp VTL appliance.

Easy to use: The existing backup and restore process need not be altered because the virtual tapelibraries of the NetApp VTL function in the same way as physical tape libraries (including the waythey are displayed to backup applications). Data can be backed up to the disk using the existinginfrastructure and work procedures.

3.1.1 Backup Workflow

The following table lists the steps in the VTL backup workflow:

Step Action

1. The backup application determines which tape (identified by the barcode) is to be used for backup.

2. The backup application controls the virtual robot to move a virtual tape from a virtual slot to a virtual tapedrive.

3. The backup application instructs a media server (also called storage node by some backup applications) tomount the tape, and starts streaming data. It continues until one of the following occurs:

The virtual tape is full.

Backup of the streaming data is completed.

4. The backup application unmounts the virtual tape and controls the robot to move the tape from the virtualdrive to a virtual slot.

Note: This workflow is the same for a NetApp VTL or a standard physical tape library.



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3.2 Hardware Overview

The figures provided in this section illustrate the hardware overview of VTL300, 700, and 1400.

Figure 3 is an example of VTL integration in a typical backup environment:

Example: NetApp VTL Backup Solution Setup

Figure 3 - NetApp VTL backup solution setup example



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Figure 4 through Figure 7 display the hardware layout of VTL300/700/1400:

NetApp VTL300 Connectivity Diagram

Figure 4 - NetApp VTL300 connectivity diagram



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NetApp VTL300 Port Locations Diagram

Figure 5 - NetApp VTL300 locations diagram

NetApp VTL700 Connectivity Diagram

Figure 6 - NetApp VTL700 connectivity diagram



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NetApp VTL700 Port Locations Diagram

Figure 7 - NetApp VTL700 locations diagram

Note: VTL7700 supports different configurations (for example, the use of some of the disk ports for tapeconnections). Contact a NetApp Professional Service representative for details.

3.3 NetApp VTL Deduplication (VTL 6.0 and Later)

Deduplication is a VTL feature that enables the amount of data to be reduced by storing only uniquedata blocks inside one or more backup data set. VTL compares blocks inside data sets and storesunique blocks (that is, blocks that are not redundant inside the data set), and stores only a pointer forother replicas of those unique blocks.

Deduplication can substantially increase virtual tape capacity, but the effectiveness is highly dependenton the data set. The deduplication process results in some reduction in read and write performance, soyou might need to choose when and for which tapes and libraries deduplication is used. With VTL 6.0,virtual tapes can use hardware compression or deduplication with hardware compression.

Like all compression techniques, deduplication works better on some types of data than others, and canuse system resources in a way that reduces maximum read and write speeds. VTL 6.0 lets you monitor

the effectiveness of deduplication, enable or disable deduplication for virtual libraries and tapes, andcontrol the timing of the deduplication processing.

VTL 6.0 implements postprocessing deduplication. In VTL 6.0 with deduplication enabled, data is writtento the virtual tapes without being deduplicated. During a postprocessing window, the appliancecompares the data on the original virtual tape to the existing copies of data within the storage pool, andcreates a deduplicated copy of the tape. The comparison is across all data in a storage pool, includingthe data in any virtual tapes that is not deduplicated.

Optionally, if cloning is configured, the data is cloned to the physical tape before starting thededuplication process. Separately, after the deduplication, the space used by redundant data isreclaimed. While data from a deduplicated tape is being written to a physical tape (for example, during



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tape export), the data is expanded back to the original data. Data might also need to be expanded if thevirtual tape is moved from a virtual library with deduplication enabled to the one with deduplicationdisabled, or to a different storage pool.

Postprocessing takes place during the postprocessing window. You can control the size and timing ofthe postprocessing window from the Configuration Tasks: Miscellaneous Dedupe Configurationscreen. You can control a postprocess window so that it starts after the backups are complete, and islarge enough to complete the tasks before the window closes. The default is 6:00 a.m. to 6:00 p.m.Tasks that start, but have not completed before the window closes, continue to run, but are throttled toreduce impact on backup performance. Tasks that are in the queue but not started remain in the queueuntil the next window.

Postprocessing tasks include the creation of the deduplicated copy of virtual tapes, migration of tapesfrom one library to another, virtual tape format conversion, and space reclamation (Free Space Build(FSB) tasks). You can enable or disable the automatic running of the postprocessing tasks from theDedupe Configuration screen. From this screen, you can also manually trigger the deduplication tasksand the FSB tasks.

You can monitor and control specific postprocessing tasks from the Daily Tasks: Monitoring Deduplication Tasks screen. This screen lists all the queued and recently completed tasks, their status,and provides an action field from which you can perform actions such as suspending or deleting tasks.You can monitor the deduplication status of individual tapes, including whether the tape is deduplicated,and what the deduplication compression ratio is, from the Configuration Tasks: Virtual Tapes Virtual

Tape List screen.

3.3.1 Requirements for Effective Deduplication

NetApp recommends using two compression cards per controller on all VTL models (300/700/1400) foreffective deduplication.

In VTL 6.0, the benefits of deduplication increase over time. Deduplication enables longer backupretention on disk. For this reason, deduplication does not necessarily reduce the number of disksrequired to store the data.



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Figure 8 shows an overview of the deduplication behavior over time:

Figure 8 - Dedupe ratio

Note: The preceding figure is meant to illustrate deduplication concepts and is based on industry

averages, not on specific tests run with NetApp VTL. The actual deduplication ratio is highly variable,depending on your backup environment and specific data sets.

Figure 8 shows four consecutive full backups for different types of data. The deduplication ratioincreases over time and gets higher, if more full backups are retained on the VTL. This example hasfour backups; however, you can get better ratios (such as, 20:1 and higher) with more backup copiesretained on the VTL. Data on physical tapes is not deduplicated because the physical tapes mustremain in the same format created by the backup application. Physical tapes can be read directly by thebackup application if needed.

Deduplication effectiveness depends on many factors (such as how much data redundancy is present inthe data that is being backed up).

The following data sets benefit the most from deduplication:

Full backups Database backups

The following data sets generally do not benefit much from deduplication:

Data that is multiplexed by the backup application (multiple backup streams sent to one virtual tapedrive)

Data that is compressed or encrypted on-the-fly by the backup application



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Note: It is possible to modify the backup application settings so that all of the data gets full benefits ofdeduplication. For details, see Chapter 4 General Best Practice Recommendations.

3.3.2 What is Different in VTL 6.0

The added features in VTL 6.0 versus VTL 5.x are as follows:

VTL 6.0 supports data deduplication.

Deduplication and non-deduplication can co-exist on the same VTL appliance. A per-virtual library option to deduplicate only shadow tapes is available.

5.x virtual tapes can be converted and deduplicated.

Imported virtual tapes are immediately compressed and can be scheduled for deduplication as well.

Overallocation is always enabled.

This allows space to be made available after the deduplication process.

3.3.3 Deduplication Configuration and Monitoring GUI Overview

This section describes the NetApp VTL GUI changes in VTL 6.0. Refer to Chapter 5 VTL Monitoringfordetails about the VTL 5.x GUI.

The features of deduplication configuration and monitoring GUI are as follows:

With VTL 6.0, deduplication is enabled at the VTL appliance level (Figure 9):

Figure 9 - NetApp VTL options

You can enable deduplication at the virtual library level.

Add or update virtual library pages support a new disk compression type called Deduplication.

Deduplication scope can be limited to shadow tapes only.

After deduplication is enabled on a virtual library, it cannot be turned off.



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Figure 10 highlights the possibility of selectively turning on deduplication on virtual libraries:

Figure 10 - Virtual library list

You can monitor deduplication tasks from the new Monitoring tab Deduplication Tasks (Figure 11).

Figure 11 - Deduplication tasks

The Virtual Tapes page now provides the following additional columns:

Need to Dedupe: This indicates that backup data is appended to this virtual tape; thereforepostprocess deduplication is needed.



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Disk Compression: This specifies either Hardware Compression or Deduplication.

See Figure 12:

Figure 12 - Virtual tape list

A new Dedupe Configuration page is added to the VTL GUI. This page also enables you to manuallystart the postprocess window or manually run an FSB task (Figure 13):

Figure 13 - Dedupe Configuration page

3.3.4 VTL 6.0 Workflow Example

An example of a typical VTL 6.0 workflow is a virtual tape that is unloaded from a virtual drive after abackup.



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This causes a postprocess deduplication task to be scheduled.

With the default settings (a postprocess window of 6:00 a.m. to 6:00 p.m.), the deduplication doesnot start until 6:00 a.m., the next day.

If any data is added to the same or other virtual tapes, the deduplication task is updated(postprocess deduplication is now scheduled to occur on two or more virtual tapes).

When the postprocess window starts (at 6:00 a.m.), the following steps are performed:

a. A deduplication task is started.

b. An FSB task is started after completing the postprocess task.

You can explicitly abort or restart tasks from the Deduplication Tasks page (see Figure 11) byclicking the Action hyperlink.

Volumes processed within a deduplication task can be removed by following the Task ID hyperlink.

If the volume is removed from an active deduplication task, the task is implicitly aborted.

3.3.5 VTL Duty Cycles

As mentioned earlier, the presence of a deduplication feature in VTL 6.0 introduces a new workload forthe VTL so that the duty cycles are changed.

The following steps are performed as part of duty cycles on VTL 5.x:

1. Backup is typically within a window, which is the primary cycle.

2. DTC (exports/clones) is performed outside the backup window. This is another cycle.

3. The VTL typically performs backups followed by a DTC.

Figure 14 shows the duty cycles in VTL 5.x:

Figure 14 - Duty cycles in 5.x

The following steps are performed as part of duty cycles on VTL 6.0:

1. VTL 6.0 adds background tasks as a cycle.2. Background tasks include postprocess deduplication and FSB process.

There is a deduplication window in addition to the backup and clone/export window. Deduplication is aCPU and I/O intensive operation. As a general rule, the combined effect of backup, DTC (if any) anddeduplication operations must not exceed the processing capabilities of a VTL controller over the 24-hour time interval (that is, duty cycle).

Figure 15 shows the duty cycles in VTL 6.0 with deduplication enabled:



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Figure 15 - Duty cycles in 6.0

Note: In practice, there might be an overlap between the different cycles. Overlapping cycles might impactperformance. The important part is to monitor the amount of backup data sent to the VTL so that all thethree cycles can complete in a 24-hour window for daily backups. Depending on your backup environmentrequirements, the window might be larger for weekend backups.



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4 General Best Practice Recommendations

4.1 NetApp VTL Compatibility List

Ensure that all the components of the backup environment appear on the NetApp VTL CompatibilityList:

http://now.netapp.com/NOW/products/osn/vtl/nearstore_vtl_compatibility.pdf

If any component in your environment is not in this list, contact your NetApp sales representative.

4.2 AutoSupport

NetApp highly recommends enabling the AutoSupport feature of the VTL. AutoSupport can beconfigured to use HTTP, HTTPS, or e-mail.

If e-mail size is a concern, see the AutoSupport section in the NetApp VTL Troubleshooting Guide.

If sending information to NetApp is a concern (such as secured site), NetApp recommends enabling thefollowing notifications:

Configure internal VTL e-mail notifications:

Enable network communications between the VTL and your e-mail server.

Set up VTL to send short e-mail notifications in case of a warning or error message (using theMiscellaneous GUI page).

Configure internal VTL AutoSupport e-mails:

Enable network communications between the VTL and your e-mail server.

Set up AutoSupport to be sent to an internal e-mail address (using the Support Tool GUIpage).

4.3 VTL Serial Console

VTL serial console is required for several maintenance and troubleshooting operations.

NetApp highly recommends connecting the VTL serial console port on a permanent basis to either ahost port or a remote serial console device. This is especially critical when a VTL is managed remotely.

NetApp recommends the following as best practices:

Option 1: Connect the serial ports of all NetApp VTL appliances to remote console devices.

Option 2: Connect VTL serial console ports to UNIX or Window hosts for remote access:

Use the serial cable shipped with the VTL or order a longer one if needed.

Set up the serial port on the host (9600, 8, none, 1, none).

The serial ports settings (for both options) are defined in the following Knowledge Base article:

https://now.netapp.com/Knowledgebase/solutionarea.asp?id=kb15972

4.4 When to Reboot a VTL

NetApp recommends the following as best practices while rebooting a VTL appliance in the event of anissue:

Do not reboot a VTL appliance unless needed.

Before rebooting a VTL, attempt all possible steps to troubleshoot the issue.

Before rebooting a VTL, collect all required diagnostics to diagnose the issue (the type ofdiagnostics varies widely as per the issue).

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Refer to the VTL Troubleshooting Guidefor details.

4.5 Backup Application Multiplexing

This section provides information about using the backup application multiplexing feature. The backupapplication might send backup streams from multiple backup clients to one virtual tape drive. As far as

VTL is concerned, this is one single data stream Figure 16):

Figure 16 - Multiplexing

Multiplexing is designed to allow a backup application to back up a large number of simultaneous clientsto a small number of physical tape drives.

With VTL, this feature is less useful as more virtual tape drives can be created.

Reducing or eliminating multiplexing whenever possible is generally recommended when the backupsare directed to a VTL, for the following reasons:

While multiplexing improves backup performance when writing to physical tapes, it is not required toget high-backup performance from a VTL (unless backups are from a large number of slow networkclients).

Multiplexing negatively impacts the restore performance.

If you are using VTL 6.0 or you plan to upgrade to VTL 6.0 in the future, NetApp highly recommendsturning off multiplexing. Deduplication is generally not very effective if data is multiplexed. Seesection 4.6.3 VTL 6.0for more specific recommendations about multiplexing.

Removing multiplexing in a VTL DTC environment has a downside, especially for incremental backups.It increases the number of virtual tapes and matching physical tapes required for backups.

In some configurations, it might make sense to do nonmultiplexed full backups and database backups,while keeping the incremental or differential backups multiplexed.



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4.6 Stream Count Recommendations

Every simultaneous backup, restore, import, or export operation consumes resources on the VTLappliance, and the resources are limited. Improvements are incorporated at various release levels asindicated in the following sections.

Note: Because backup application multiplexing is independent of the VTL (that is, a multiplexed datastream counts as one single I/O stream while hitting the VTL), any number of multiplexed streams can besupported. See section 4.5 Backup Application Multiplexingfor recommendations regarding multiplexing

with VTL.

In this context, a stream is a stream of data from the backup application server to a VTL virtual tapedrive. It is not a stream of data from a backup application client to a backup application server. A backupapplication server can multiplex streams of data from several backup clients and produce a singlestream to the VTL.

4.6.1 VTL Releases Prior to 5.5

NetApp VTL appliances prior to VTL 5.5 support 64 simultaneous backup streams (note that a loadedvirtual drive, even if inactive, is treated as a backup stream). Each simultaneous export/clone to tapereduces this by one. Each simultaneous import from tape reduces this by two.

4.6.2 VTL 5.5 and 5.6

VTL 5.5 and 5.6 support up to 90 concurrent streams. A virtual tape loaded in a drive for backup orrestore purpose can be accounted as one stream. Each import, export, or clone operation uses onestream.

If the backup application attempts to create backup streams in excess of the limit (90), the applianceissues the following event log message:

event 405, Library a: Tape 000 failed to load into drive Drive0:

Total loaded drives and active import/export requests exceed the limit (90).

NetApp recommends testing a backup schedule for adequate performance before using it in aproduction environment.

If loading a virtual drive is attempted and no streams are available, the virtual tape will be moved to thedrive but the load will fail. From a backup application perspective, the virtual tape is in the drive but if I/Ois done to the drive, it gets an error message stating that there is no media in the drive.

DTC actions (clone, export, or import) become active only if a stream is available. If no streams areavailable, new export/import requests simply accumulate in the queue.

A large number of streams are not required for maximum VTL performance; therefore, NetApprecommends between 16 and 64 concurrent streams.

More than 64 virtual tape drives can be created and configured, if needed to be used by thebackup/media servers. For example, a total of 100 virtual tape drives can be created in VTL and zonedto the backup/media servers. Depending on the backup schedule, the maximum number of drives usedat a given time might be 50. If the VTL is configured to do cloning to 10 physical tape drives (and the

cloning occurs during the backup window), the actual number of concurrent stream will not exceed 60.

4.6.3 VTL 6.0

VTL 6.0 introduces new postprocessing tasks so that the streams count and allocation changes slightly.The following concurrent tasks and streams are supported in VTL 6.0:

Maximum stream count is 96 (this limit is enforced, like in VTL 5.5/5.6).

The following workflows account for one stream:

A virtual tape loaded in a drive for backup/restore operation

A clone, export, or import operation



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The following workflows account for two streams:

A format conversion (upgrade) task

A migration task (migrates data to a different storage pool)

Up to 10 virtual tapes can be processed concurrently, counting as 20 streams.

A deduplication task accounts for 2 to 16 streams:

One single postprocess deduplication task (per storage pool) runs at a time.

The deduplication task uses two streams per RAID group, up to a maximum of 16 streams.

FSB does not account for any stream:

Only one FSB task (per storage pool) runs concurrently.

FSB task does not contribute to the 96 streams.

Note: Postprocess deduplication and FSB tasks cannot run concurrently.

NetApp recommends the following as best practices:

The maximum number of concurrent streams for VTL 6.0 is similar to the ones for VTL 5.5/5.6 releases.If there is an overlap between the backup window, the clone/export window, and the postprocesswindow, the additional streams required by postprocess deduplication must be taken into account (up to16 streams depending on the number of RAID groups).

VTL 6.0 supports data deduplication. Data deduplication might be ineffective if the data is multiplexedby the backup application. Therefore, NetApp recommends turning off the backup applicationmultiplexing when deduplication is used.

Depending on the backup environment, some level of multiplexing might be needed to reduce thebackup window. Incremental backups tend to generate less data on each client and multiplexing datafrom several clients might be required to obtain adequate backup performance.

If this is the case, VTL is configured as follows:

Enable deduplication on one virtual library and direct the following backups to this virtual library:

Unmultiplexed full or incremental database backups

Unmultiplexed file system full backups

Enable hardware compression on a second virtual library and direct the following backups to thisvirtual library:

Multiplexed file system incremental backups

Having two virtual libraries with VTL 6.0 has another possible advantage. In case of DTC, shadow taperetention can be set to different values on the two virtual libraries. This is useful as an example in caseyou want to keep full backups longer than incrementals.

Note: Other configurations are more appropriate for the specific backup environments. Work with aNetApp Professional Service representative to define the configuration most suitable for your environment.

4.7 Virtual Tape Drive Unload/Unmount Policy for VTL 6.0

Backup applications are designed to work with physical libraries. Some backup application might leavevirtual tapes in drives for a while after a backup is complete. This is generally a configurable setting.

With VTL, there is no benefit in leaving virtual tapes in drives. With VTL 6.0, there is one more reason tonot leave virtual tapes in drives after a backup or restore operation: A virtual tape does not getscheduled for deduplication until it is unloaded from a drive.

4.8 Tivoli Storage Manager

This section is specific to backup environments using IBM

Tivoli

Storage Manager as a backupapplication.



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4.8.1 General Considerations

1. Barcode Naming Conventions

Tivoli Storage Manager does not support upper case letters for tape barcodes. Ensure that you uselower case letters (and numbers) while creating virtual tapes.

2. Tivoli Storage Manager does not Support Multiplexing on Sequential Devices

This is an architectural limitation of Tivoli Storage Manager aimed at improving restore speed from

sequential devices (no data multiplexed, all data coming from a single stream and contiguous on tape).With a large number of client sessions running in parallel, there is normally a need for a disk-based pool(Tivoli Storage Manager cache or staging) before moving data to sequential devices.

To improve performances and eventually get rid of Tivoli Storage Manager disk pools for data stored onVTL, you need to create a large number of virtual drives to handle all the sessions and avoid queuing.When doing this, keep in mind the VTL concurrent streams limitations discussed previously (90 or 96depending on VTL versions).

This aspect also impacts the choice of the virtual tape size that must be a compromise between theavailable space, the number of concurrent tapes to mount and the overall VTL configuration (that is, themaximum number of virtual tapes, currently set at 10000, deduplication, and so on).

Note: NetApp highly recommends Professional Service consulting for deploying VTL in a Tivoli StorageManager environment. This document attempts to provide general guidelines, which might not apply toyour specific environment.

3. Supported Emulations

NetApp and IBM are supporting the following configurations for Tivoli Storage Manager:

Table 1 - Tivoli Storage Manager configurations

TSM 5.5.1Backup Server OS AllLibrary Type NetAppTape Drive Type IBM LTO4 or STK T10000A

TSM 5.5

Requires the latest 5.5 patch (currently 5.5.0.3)Requires specific changer types.

Note: This information is subject to change. For up-to-date information, refer to the NetApp VTLCompatibility List at http://now.netapp.com/NOW/products/osn/vtl/nearstore_vtl_compatibility.pdf.

4.8.2 Virtual Library Configuration

Tivoli Storage Manager uses Element Addresses (also named Element IDs) to manage libraries(regardless of whether they are virtual or physical ones). Each element inside a library (library robot(s),tape drives, slots and I/O slots) has its own Element Address. Tivoli Storage Manager cannot managethe library properly if this value changes.

For this reason, changes to a virtual library layout require Tivoli Storage Manager reconfiguration. Toavoid reconfiguring at a later time, NetApp recommends sizing a virtual library to be used by StorageManager for future growth. This implies creating more slots and drives in the virtual library than initiallyneeded. Some of the drives can be initially hidden from the Tivoli Storage Manager server by using theVTL Port Assignment, the Host Access Control features, or both.

The user must define the drives on the Tivoli Storage Manager server to access storage volumes, byusing the DEFINE DRIVE and DEFINE PATH commands or through the management console.

The following variables might be needed to define the drives:

Library Name: the name of the library where the drives reside

Drive Name: the name assigned to the drive

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World Wide Name: the Fibre Channel worldwide name for the device

Serial Number: only applies to the drives in SCSI libraries and can be assigned manually, or aparameter AUTODETECT = YES can be defined to allow the server to manually correct the serialnumber entered.

Element Address: the ELEMENT parameter represents the physical location of the drive within anautomated library. The server can be allowed to pick up the element number from the drive itself or itcan be specified while defining the drive. Element numbers for many libraries are available in the

following link:www.ibm.com/software/sysmgmt/products/support/IBMTivoliStorageManager.html

Some libraries might not support auto-detect of the element address by the Tivoli StorageManager server. In these circumstances, an element address (number) must be specified duringdrive definition to a higher range to avoid conflicts from the existing devices or possible changes tothe SAN infrastructure.

Note: Auto-detect is supported for virtual libraries of the type NetApp VTL.

Each tape library vendor has an assigned offset for its libraries. So the element ID is made by thereal element ID inside the library + the vendors own offset.For example, a Quantum library has an offset of 4092, so it can a have robot (address 0) with ID4092, drives (addresses 1-4) with 4093-4095 and so on.

4.8.3 Tivoli Storage Manager Mount Retention Settings

NetApp recommends setting Tivoli Storage Manager mount retention to 0 when backups are directed toVTL. This causes Tivoli Storage Manager to immediately unload a tape from virtual drives after abackup to this tape is completed.

There is no benefit in leaving virtual tapes in drives, because the load/unload operation is instant with aVTL. Unloading a virtual tape from a drive after doing a backup to this virtual tape causes VTL to flushthe data to disk immediately.

For details, refer to the following Knowledge Base article:


4.9 Physical Library SharingOne VTL appliance requires a dedicated physical library or partition (except if using ACSLS). Unless aphysical library is managed by Sun ACSLS software, a VTL appliance is expected to control the entirephysical library.

The only way to share a non-ACSLS-managed physical library is to partition the library. Most physicallibrary vendors support library partitioning through specific software. Each physical library partitionappears as a separate physical library to VTL, effectively allowing library sharing by several VTLappliances, and/or sharing with other applications.

See also the following Knowledge Base article:


4.10 Number of Initiators per VTL Port

While there is no hard limit on the number of backup or media server ports that can be connected to aVTL, NetApp recommends the following:

Do not connect more than four initiator ports to each VTL port.

Spread backup or media server connections to all VTL front-end ports (make port 0d a front-end portif needed).

Each (initiator port, VTL port) pair must be in its own Fibre Channel zone.

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If several initiator ports are connected to a single VTL port, enable and configure VTL host accesscontrol.

4.11 Virtual Tape Record Size

VTL supports a maximum block size of 2-MB. Virtual tapes with 256-KB, 512-KB, and 1-MB block sizeshave approximately the same level of efficiency.

NetApp recommends the following as best practices:Some physical tape drives do not support a block size larger than 256K. As increasing the tape recordsize beyond 256K does not yield a significant performance gain, set the record size used by the backupapplication to 256K.

4.12 Enable VTL HTTP and SSH Ports

Some customer network environments have restrictions in using the HTTP port for security reasons.

VTL uses the following HTTP ports:

Port 80: This is the default web port that is used with a normal VTL GUI access.

Port 8888: This is the VTL diagnostics web server that is required for troubleshooting.

Port 9999: This is an alternate port for the regular VTL GUI. It is generally not required.

Note: SSH ports must also be enabled to use the VTL CLI from a host. Even if the VTL is primarilymanaged through the GUI, the CLI can be an important tool for troubleshooting. Therefore, NetApprecommends enabling SSH TCP/IP port as well. VTL uses the default SSH port.



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5 VTL Monitoring

Monitoring a NetApp VTL appliance and any attached devices involves viewing the amount of diskspace used, the data transfer rates, physical tape drive information, import/export requests, event loginformation, and any actions required.

5.1 Administrator OverviewThis section provides information about the current state of the NetApp VTL appliance. Figure 17 showsthe main monitoring screen. It displays information about the amount of disk space allocated to andused by the NetApp VTL, actions required, the system event log, and so on. It also provides links to theActions Required, Event Log screens, and Statistics and Import/Export requests.

Figure 17 - Administrator Overview screen

5.2 Actions Required

See the VTL Administration Guidefor a full list of required actions. It also provides an interface foracknowledging and resolving required actions.

See also the VTL Troubleshooting Guidefor a list of the most frequent action codes, and more detailson how to resolve them.

5.3 Notifications

Perform the following steps to enable VTL notifications:



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1. Enable VTL e-mail notifications.

2. Enable network communications between the VTL and your e-mail server.

3. Set up the VTL to send short e-mail notifications in case of a warning or error condition (using theMiscellaneous GUI page).

4. Enable VTL AutoSupport e-mails.

5. Set up AutoSupport to send e-mails to NetApp and to a customer-internal address (using theSupport Tool GUI page).

Alternatively, set up AutoSupport to send notifications only to NetApp HTTP or HTTPS.

6. If an SNMP-based management framework is used, set up the VTL to send SNMP traps in case ofwarnings or error messages. Traps can be filtered by the management framework.

See the following Knowledge Base article for details:


5.4 Statistics

This section provides specific I/O statistics for each device used by the NetApp VTL. This includes bothvirtual and physical devices.

Figure 18 shows the Statistics screen:

Figure 18 - Statistics screen

Use the Statistics screen to monitor specific I/O statistics for both the physical and virtual devices thatare in use by the VTL appliance. For example, you can check the amount of disk space currently

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allocated to and used by a specific virtual library using the Statistics page. This screen also provides thetype of virtual tape drives that are being used by the virtual library.

This information is helpful in determining the state of the virtual library, including its compatibility withother virtual and physical media, based on the type of virtual tape drive being used. From the DailyTasks menu, located on the left side of the screen, click Monitoring Statistics. The Statistics screenappears. This screen is divided into the following three sections:

Virtual Library I/O Load

RAID Group I/O Load

Physical Tape Device I/O Load

You can find the VTL MIBs at http://now.netapp.com/NOW/download/tools/mib/#vtl

5.4.1 Virtual Library I/O Load

The following items are listed on the Virtual Library I/O Load page:

Library: provides the name of the virtual library.

Allocated: specifies the amount of disk space that is allocated to the virtual l ibrary.

Used: provides the total amount of user data stored on the virtual tapes associated with the virtuallibrary.

Data Written: provides the total amount of user data stored on the virtual tape. Drive: provides the number of virtual tape drives in the virtual library.

Tape Label: if a virtual tape is currently loaded in the virtual tape drive, the VTL displays the label ofthe virtual tape. If no virtual tape is loaded, the VTL displays Empty. The label of a virtual tape is itsbarcode.

Mode: specifies the mode of the virtual tape drive.

The following are the valid modes:

Write: the host is either currently writing to the drive or it has not sent any commands since itlast wrote to the drive.

Read: the host is either currently reading from the drive or it has not sent any commands sinceit last read from the drive.

Idle: the drive is not currently being used.

N/A: the library is not loaded in the drive.

IO/Sec: provides the total number of operations per second for the drive.

MB/Sec: provides the data rate in megabytes per second for the drive.

Load Factor: provides (in percentage) the I/O load of the virtual tape drive. A lower percentageindicates that the VTL is waiting more on I/O from the host side, while a higher percentage indicatesthat the VTL is waiting less on I/O from the host side.

Used: provides the amount of user data stored on the virtual tape loaded in the virtual tape drive.

Active Disk: specifies the disk from which the host is either reading or writing data.

5.4.2 RAID Group I/O Load

The following items are listed on the RAID Group I/O Load page:

Drive: provides the name of the back-end physical disks in the RAID group.

Capacity: specifies the capacity of each disk.

Used: gives the amount of disk space that is currently used.

System Overhead: specifies the amount of disk space being used for system overhead.

IO/Sec: provides the number of operations per second for the disk.

MB/Sec: provides the data rate in megabytes per second for the disk.

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5.4.3 Physical Tape Device I/O Load

The following items are listed on the Physical Tape Device I/O Load page:

Drive: provides the name of the physical tape drive.

Tape: provides the barcode of the physical tape that is currently loaded in the drive.

MB/Sec: specifies the transfer rate of the physical tape drive.

5.5 Import/Export Requests

Import/export requests provide a list of all physical tapes that need to be mounted to physical tapedrives. If a hard tape error occurs during an export/clone operation from the VTL to a physical library,the export/clone operation is failed and an action required request is generated. You have the option toretry or cancel the job. If the retry fails, put the same barcode on a new tape and retry again, or use thebackup application to clone it to a different virtual tape.

5.6 Event Log

Event log provides a list of events for the NetApp VTL. Event log information includes the time and codeof the specified event. The view is only a partial log. You can view additional logs by clicking theprevious page link or clicking the Upload Complete event log.

5.7 Deduplication Tasks (VTL 6.0)

Deduplication tasks (also called background tasks as they are automatically scheduled by default) inVTL 6.0 appliances run daily.

5.7.1 Background Tasks

VTL OS 6.0 introduces background tasks that are related to deduplication. Background tasks are usedto perform regular postprocessing of data stored on disk. These tasks are initiated either automaticallyor manually. A window is configured so that the tasks run when other operations (such as backups orclones) are completed.

The major background tasks include:

Deduplication

Self deduplication (within and across volumes in the same deduplication request)

Storage pool-wide deduplication

Verify

Verify is a troubleshooting tool used only when directed by NetApp customer support.

Free Space Build (FSB)

On-disk space saved during deduplication is made available for reuse.

It runs by default after deduplication.

Deduplication effect is visible after the FSB task through compression ratio.

Note: Virtual tapes can be appended to or overwritten by the backup application during postprocessing.

5.7.2 Postprocessing Window

You can define the postprocessing window settings when tasks are appended to the execute tasks list.When the window closes, if backgrounds tasks are running, an event is generated to notify theadministrator and the task continues to execute until it is complete. Postprocessing windowconfiguration is located under Configuration Tasks Miscellaneous Dedupe Configuration (Figure19):



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Figure 19 - Dedupe Configuration screen

5.7.3 Deduplication StatusYou can check the status of deduplication tasks on the Deduplication Tasks screen. DeduplicationTasks are located under Daily Tasks Monitoring Deduplication Tasks. The Deduplication Taskspage shows the task with its description and status. Action includes a link for active and idle tasks,which allows tasks to be aborted or modified (Figure 20):

Figure 20 - Deduplication tasks

5.7.4 Task Management

You can manage the deduplication tasks from the Monitoring page. You can perform the following taskoperations on the Monitoring page:

Suspend, resume, delete, or abort deduplication tasks

Remove virtual tapes from a postprocessing request

Completed tasks are removed from the VTL GUI after 24 hours. Failed tasks are kept on the GUI untilthey are successfully retried or deleted.



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5.7.5 Deduplication Task Scheduling

A virtual tape is marked with a needs dedupe flag after data is appended, or overwritten, andunloaded from a drive. If cloning is enabled on the virtual library, the cloning operation is scheduled first.After it is cloned to a physical tape, this virtual tape is scheduled for postprocess deduplication.

One single postprocess deduplication request includes many virtual tapes. A postprocess deduplicationtask, which is scheduled before the postprocess job window opens, is started during this postprocessingwindow (unless another deduplication task runs in the window). Tasks (of any type) scheduled during a

postprocessing window can be started either during this window or the next postprocessing window.Postprocessing can also be started manually.

5.7.5.1 Manually Start Tasks

To manually start background tasks, use the Dedupe Configuration tab. Click the here link to start allscheduled tasks (Figure 21):

Figure 21 - Dedupe Configuration screen

5.7.5.2 Scheduling Free Space Build (FSB) Task

An FSB task is automatically started after the postprocessing task is complete.

Only one FSB task per storage pool can run at a given time. For manually starting an FSB task, a link isavailable on the Dedupe Configuration page. An FSB task is automatically triggered when a storagepool is low on disk space. Free disk space is reclaimed only after the FSB task is complete.

5.8 Capacity Management

This section provides details about the capacity management of VTL appliances.

5.8.1 VTL 5.5/5.6 without DTC or Overallocation

This section details the best practice recommendations for VTL setups without a back-end physicallibrary. NetApp recommends the following as best practices in terms of VTL space allocation:

Keep the compression enabled on the virtual library and keep the disk utilization around 90-92% (itis the best practice in any storage or backup device). Exceeding this limit can lead to performanceslowdown due to the lack of free space available to write new data (this is not a pure VTL behaviorbut rather standard storage behavior, due to the way in which a storage subsystem writes data toRAID groups).



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Only a field test can evaluate the differences in disk utilization that can be achieved.

As a general rule, there must be a 10% unused disk space to ensure good performance. This is alsoa best practice for having some contingency.

An example of contingency is a degraded RAID group. If a RAID group goes into degraded modebecause of a failed disk, the available disk space might be adversely affected. NetApp recommendsthat, for VTL to function properly, there must always be at least two RAID groups of disk space (or10% of the total configured disk space) available. Allowing one or two RAID group to go offline

without exceeding this free space is a good policy in environments with critical uptimeconsiderations.

5.8.2 VTL 5.5/5.6 with DTC and/or Overallocation

Overallocation is an optional VTL feature. If overallocation is not enabled, NetApp VTL automaticallyreserves enough disk space for any virtual tapes that you create. For example, if you create a virtualtape with a 40-GB capacity, NetApp VTL reserves 40 GB of space for that virtual tape from a storagepool. If you want to create 10 such tapes, you need 400 GB of available disk space.

If you enable overallocation, NetApp VTL allocates disk space to virtual tapes as needed, regardless ofhow many volumes you initially create. This feature is sometimes called Capacity on Demand. Enablingoverallocation provides the best disk and tape utilization, but increases the chance of running out ofspace. Although the VTL generates actions when available space is low (and if shadow tape is in use itwill try to recover space), close monitoring is required to prevent low available space. If the disk capacityreaches 100%, an alert is generated, and any further attempts to write data will result in failures thatimpact the backup application. Also, note that if overallocation is used, problems such as a disk failureare more likely to cause the appliance to run out of available space.

As a general rule, VTL disk usage must not exceed 85% of capacity. The recommendation here is alittle more conservative because of the following considerations:

Overallocation bypasses the normal capacity checks and lets the user create virtual tapes beyondthe actual disk space available on the VTL.

A temporary slowdown in VTL back-end activity (such as, a physical tape drive is down) might meanthat more data needs to be stored on the VTL.

Note: After overallocation is enabled on a VTL appliance, do not change this setting.

The following action required message is created when the VTL disk usage approaches the totalavailable capacity:

VTL Action Code 1300: Disk usage is nearing capacity.

This Action Code indicates that the available disk space to save more user data is very low. The alert istriggered at 90% of total capacity. This condition does not cause any danger to the existing data that isstored inside the VTL.

At this point, the VTL begins to purge shadow tapes if they exist. If the user continues to write data tothe VTL without resolving this problem, VTL stops storing the new user data when it reaches its capacityand all the backups will fail.

Use the following methods to resolve this:

Export some of the virtual tapes to free up more space. When the export is complete, the virtual tapeis deleted (or moved to the shadow pool if configured to do so and shadow tapes are automaticallydeleted when the VTL disk usage is nearing capacity).

Backup applications only track and write to media, they do not delete the contents of media(physical or virtual tapes). Tapes expired or deleted in a backup application are marked as such inthe backup application's media database (catalog) only. Use the backup application to zero out(label or quick erase) the expired media. If a backup application has a virtual tape that is prev

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