comptia server plus courseware instructor sample

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CompTIA Server+ Certification Support Skills (2009 Objectives)

Instructor Edition Study Notes

G601Teng ver062

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Tel: +44 (0)20 7887 7999 Fax: +44 (0)20 7887 7988 Email: [email protected]

Acknowledgements

www.gtslearning.com

Course Developer ......................................................... gtslearning

Editor ..................................................................... James Pengelly

This courseware is owned, published, and distributed by gtslearning, the worlds only specialist supplier of CompTIA learning solutions. [email protected] +44 (0)20 7887 7999 +44 (0)20 7887 7988 Three Elysium Gate, 126-128 New Kings Road, London, SW6 4LZ, UK

COPYRIGHT

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CompTIA Server+ Certification Support Skills (2009 Objectives) Table of Contents

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Table of Contents

Course Introduction i

Table of Contents ............................................................................................................. iii About This Course .......................................................................................................... viii

Module 1 / Planning Servers 1

Module 1 / Unit 1 Server Fundamentals 3

Servers as Hardware and Software ................................................................................... 3 Server Form Factors .......................................................................................................... 8 Racks .............................................................................................................................. 10

Module 1 / Unit 2 Configuration Management 17

Project Planning Concepts .............................................................................................. 17 Server Pre-installation Planning....................................................................................... 20 Server Upgrade Plans ..................................................................................................... 24 Implementing the Plan ..................................................................................................... 26 Verifying the Plan ............................................................................................................ 27 Configuration Management ............................................................................................. 28 Documentation ................................................................................................................ 31 Equipment Disposal ......................................................................................................... 37

Module 1 / Unit 3 Storage and RAID 39

Hard Drives ..................................................................................................................... 39 The SCSI Interface .......................................................................................................... 42 Serial Attached SCSI (SAS) ............................................................................................ 52 The Serial ATA Interface ................................................................................................. 54 Drive Arrays (RAID) ......................................................................................................... 56

Module 1 / Unit 4 Installing an NOS 72

Installation Procedures .................................................................................................... 72 File Systems .................................................................................................................... 76 Installation Methods ......................................................................................................... 81 Configuring the NOS ....................................................................................................... 85 Performing Shut Down .................................................................................................... 93

Module 1 / Summary Planning Servers 99

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Course Introduction CompTIA Server+ Certification Support Skills (2009 Objectives)

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Module 2 / Configuring Servers 101

Module 2 / Unit 1 Server Networking 103

Ethernet ......................................................................................................................... 103 TCP/IP ........................................................................................................................... 108 Virtual LANs (VLAN) ...................................................................................................... 113

Module 2 / Unit 2 Directory Services 116

Configuring Directory Services ...................................................................................... 116 Managing Users ............................................................................................................ 118

Module 2 / Unit 3 File and Print Services 128

Configuring File and Print Services ................................................................................ 128 External Storage Technologies ...................................................................................... 138 Disk and Volume Management ...................................................................................... 142

Module 2 / Unit 4 Site Security 150

Designing a Secure Site ................................................................................................ 150 Site Security Controls .................................................................................................... 154

Module 2 / Unit 5 Server Security 161

Secure Network Topologies ........................................................................................... 161 Firewalls and Proxy Servers .......................................................................................... 165 Malware Protection Software ......................................................................................... 170

Module 2 / Summary Configuring Servers 175

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Module 3 / Application Servers 177

Module 3 / Unit 1 Configuring Server Roles 178

Installing Roles and Applications ................................................................................... 178 Network Configuration and Access ................................................................................ 181 Database and Application Servers ................................................................................. 191 Web and FTP Servers ................................................................................................... 193 Messaging Servers ........................................................................................................ 199

Module 3 / Unit 2 Virtualization Technologies 201

Virtualization Defined ..................................................................................................... 201 Virtual Platform Applications .......................................................................................... 204 Virtualization Best Practices .......................................................................................... 207

Module 3 / Summary Application Servers 213

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Module 4 / Managing and Upgrading Servers 215

Module 4 / Unit 1 Management and Monitoring Tools 217

Developing a Server Management Plan ........................................................................ 217 Network Management Protocols .................................................................................... 218 Server Access Tools ...................................................................................................... 223 Server Monitoring .......................................................................................................... 228 System Logs.................................................................................................................. 240

Module 4 / Unit 2 Environment and Maintenance 244

Preventative Maintenance ............................................................................................. 244 Power ............................................................................................................................ 245 Server Environment ....................................................................................................... 259

Module 4 / Unit 3 Installing and Upgrading Hardware 267

Adding and Removing Components .............................................................................. 267 Accessing the Case ....................................................................................................... 268 CPU .............................................................................................................................. 274 Memory ......................................................................................................................... 282 Expansion Cards ........................................................................................................... 291 Firmware ....................................................................................................................... 295

Module 4 / Summary Managing and Upgrading Servers 302

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Module 5 / Troubleshooting Servers 303

Module 5 / Unit 1 Troubleshooting Procedures 305

Troubleshooting Models and Processes ........................................................................ 305 Troubleshooting Steps ................................................................................................... 307 Approaching Troubleshooting ........................................................................................ 317

Module 5 / Unit 2 Troubleshooting Scenarios 319

Troubleshooting Hardware Problems ............................................................................ 319 Troubleshooting Storage ............................................................................................... 326 Troubleshooting Network Problems ............................................................................... 333 Troubleshooting Software Problems .............................................................................. 344

Module 5 / Unit 3 Disaster Recovery 350

Disaster Recovery Planning .......................................................................................... 350 Fault Tolerance and Redundancy .................................................................................. 352 Health and Safety .......................................................................................................... 357 Recovery ....................................................................................................................... 361 Backup Strategies ......................................................................................................... 364

Module 5 / Summary Troubleshooting and Disaster Recovery 378

Index 379

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About This Course

Who Should Follow This Course?

This course is intended for students wishing to qualify with CompTIA Server+ Certification for advanced level technical competency of server issues and technology. It is also suitable for PC support technicians wanting to improve their skills in support and administration.

The course has been developed to produce server support technicians who are capable of taking and passing CompTIA's Server+ Certification exam or other similar qualifications.

What are the Course Prerequisites?

Ideally, you should have successfully completed CompTIA A+ Certification and have around 12 months' experience of PC support. It is not necessary that you pass the A+ exams before completing Server+ certification, but this is recommended.

Regardless of whether you have passed A+, it is recommended that you have the following skills and knowledge before starting this course:

Know the function and basic features of the components of a PC.

Know the PC startup process.

Use Windows to create and manage files and use basic administrative features (Explorer, Control Panel, Management Consoles).

Basic network terminology (such as OSI Model, Topology, Ethernet, TCP/IP).

Optionally, you can take a prerequisites test to check that you have the knowledge required to study this course at www.gtssupport.com/flower27/SK0-003/index.htm.

Course Outcomes

The main aim of this course is to help to prepare you for CompTIA's Server+ Certification exam. Server+ Certification is internationally recognized by many corporations. Indeed, CompTIA Server+ Certification is a prerequisite qualification for employment (and is endorsed) by many leading computer manufacturers and vendors on a global basis.

This course will teach you advanced level technical competency of server issues and technology, including installation, configuration, upgrading, maintenance, environment, troubleshooting and disaster recovery.

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CompTIA Server+ Certification Support Skills (2009 Objectives) About This Course

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Study of the course can also help to prepare you for other, similar technical support qualifications and act as a groundwork for more advanced training. Other qualifications available include:

CompTIA Network+ - a foundation-level certification of competency in network installation and configuration.

Cisco Certified Network Associate (CCNA) - a foundation-level certification of competency in Cisco networking appliance installation and configuration.

Microsoft Certified Systems Administrator / Engineer / IT Professional (MCSA / MSCE / MCITP) - Windows-specific qualifications; passing CompTIAs Network+ Certification plus either Server+ or Security+ Certification can satisfy the requirements for the elective part of the certification, as well as providing a solid groundwork for the further study required for MCSA / MCSE (Windows Server 2003 track) or MCITP (Windows Server 2008 Server Administrator / Enterprise Administrator track).

Help Desk Support Analyst - The Help Desk Analyst certification series, administered by the Help Desk Institute (www.thinkhdi.com), certifies learners customer service and Help Desk management skills. Various levels of certification are available, including Customer Support Specialist, Help Desk Analyst and Help Desk Manager.

About the Course Material

The course material has been prepared as an aid for your use throughout the training course. You may keep this manual for your own reference after the course is finished. We hope you will find the course material useful for future reference.

Course Organization

This course book contains the study notes for you to refer to in class and to review at home as you prepare for the exam. The course is divided into several modules, each covering a different subject area. Each module is split into a series of units containing related topics for study. Each unit has a set of review questions designed to test your knowledge of the topics covered in the unit. Answers to the review questions are located in the companion volume.

Throughout the course, there will be ample opportunity for you to learn through practical work. A series of 'hands-on' labs help to familiarize you with the concepts and technologies that are taught on this course.

At the back of the book there is an index to help you look up key terms and concepts from the course.

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The accompanying book contains a list of the CompTIA certification objectives (and where in the study notes you can find useful material to prepare for each objective), tips for taking the CompTIA exams, the practical labs for you to complete in class, a glossary of terms and concepts used in computer support, and answers to the end of unit review questions.

When you have completed the course and want to prepare for the exam, you can take a practice test at www.gtssupport.com/flower27/SK0-003/index.htm.

Conventions Used in the Course

Certain conventions have been followed to help you use this course material. These are especially useful for following the practical lab exercises.

Bullet Points

Steps for you to follow in the course of completing a task or hands-on exercise and review questions are indicated by numbered bullet points. Other bullet points indicate learning objectives and feature lists.

File Conventions

The steps to follow to open a file or activate a command are shown in bold with arrows. For example, if you need to access the Control Panel in Windows, this would be shown in the text by:

Example: Select Start > Settings > Control Panel

Text Conventions

Commands

Commands or information that needs to be supplied by you that are entered from the keyboard are shown in Courier New bold.

Example: Type [email protected]

Displayed text and buttons

Information that is displayed on the screen by the computer is shown in sans serif bold. This includes button text and messages.

Examples: Click OK, Click Continue...

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CompTIA Server+ Certification Support Skills (2009 Objectives) About This Course

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Key to Symbols Used in the Notes

Icon Meaning

A note or warning about a feature.

More information on this topic can be found in the section mentioned.

An area for your notes.

Review questions to help test what you have learned.

A hands-on exercise for you to practice skills learned during the lesson.

CompTIA Authorized Quality Curriculum Program

The logo of the CompTIA Authorized Quality Curriculum (CAQC) program and the status of this or other training material as "Authorized" under the CompTIA Authorized Quality Curriculum program signifies that, in CompTIA's opinion, such training material covers the content of CompTIA's related certification exam.

The contents of this training material were created for the CompTIA Server+ Certification exam (exam code: SK0-003) covering CompTIA certification objectives that were current as of April 2009.

CompTIA has not reviewed or approved the accuracy of the contents of this training material and specifically disclaims any warranties of merchantability or fitness for a particular purpose. CompTIA makes no guarantee concerning the success of persons using any such Authorized or other training material in order to prepare for any

CompTIA certification exam.

This icon denotes a slide to accompany the text.

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How to Become CompTIA Certified

This training material can help you prepare for and pass a related CompTIA certification exam or exams. In order to achieve CompTIA certification, you must register for and pass a CompTIA certification exam or exams.

In order to become CompTIA certified, you must:

1) Select a certification exam provider. For more information please visit certification.comptia.org/resources/registration.aspx

2) Register for and schedule a time to take the CompTIA certification exam(s) at a convenient location.

3) Read and sign the Candidate Agreement, which will be presented at the time of the exam(s). The text of the Candidate Agreement can be found at certification.comptia.org/resources/candidate_agreement.aspx

4) Take and pass the CompTIA certification exam(s).

For more information about CompTIAs certifications, such as their industry acceptance,

benefits, or program news, please visit certification.comptia.org

CompTIA is a not-for-profit information technology (IT) trade association. CompTIAs certifications are designed by subject matter experts from across the IT industry. Each CompTIA certification is vendor-neutral, covers multiple technologies, and requires demonstration of skills and knowledge widely sought after by the IT industry.

To contact CompTIA with any questions or comments, please call (1) (630) 678 8300 or email [email protected].

It is CompTIA's policy to update the exam regularly with new test items to deter

fraud and for compliance with ISO standards. The exam objectives may

therefore describe the current "Edition" of the exam with a date different to that

above. Please note that this training material remains valid for the stated exam

code, regardless of the exam edition. For more information, please check the

FAQs on CompTIA's website (certification.comptia.org/customer_service).

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No part of these notes may be reproduced in any form, electronic or printed, without the written permission of a director of gtslearning International Limited. If you suspect that these notes have been unlawfully copied, please telephone +44 (0)207 887 7999 or email [email protected]

Study Notes Planning Servers

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Module 1 / Planning Servers

In this module, you will learn about server form factors and storage technologies. You will also learn how to plan and specify servers and document the server environment and how to install or deploy a Network Operating System (NOS).

The following table lists the CompTIA Server+ domain objectives and content examples covered in the units in this module:

Unit Domain Objectives / Examples

1.1 Server Fundamentals

1.2 Deploy different chassis types and the appropriate components Form Factor [tower, rack, blade] (Space utilization ([U size, height, width, depth]) Power buttons Reset buttons Diagnostic LEDs

2.4 Explain different server roles, their purpose and how they interact Explain the difference between a workstation, desktop and a server

1.2 Configuration Management

4.1 Write, utilize and maintain documentation, diagrams and procedures Follow pre-installation plan when building or upgrading servers Labeling Diagram server racks and environment topologies Hardware and software upgrade, installation, configuration, server role and repair logs Document server baseline (before and after service) Original hardware configuration, service tags, asset management and warranty Vendor specific documentation (Reference proper manuals, Websites, Support channels [list of vendors])

4.2 Given a scenario, explain the purpose of the following industry best practices Follow vendor specific server best practices (Documentation, Tools, Websites) Explore ramifications before implementing change determine organizational impact Communicate with stakeholders before taking action and upon completion of action Comply with all local laws / regulations, industry and corporate regulations Purpose of Service Level Agreement (SLAs) Follow change control procedures Equipment disposal

4.5 Given a scenario, classify physical security measures for a server location Secure documentation related to servers (Passwords, System configurations, Logs)

Use the gtstrainer.com website to download resources to help to setup and run this course.

If you don't have a login for gtstrainer or access to the Server+ course resources, email [email protected].

This module looks at the basic elements that need to be in place to install a server - chassis types, storage / RAID, and installing the NOS.

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No part of these notes may be reproduced in any form, electronic or printed, without the written permission of a director of gtslearning International Limited. If you suspect that these notes have been unlawfully copied,

please telephone +44 (0)207 887 7999 or email [email protected]

Module 1 / Unit 1 CompTIA Server+ Certification Support Skills (2009 Objectives)

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Unit Domain Objectives / Examples

1.3 Storage and RAID

1.3 Differentiate between memory features / types and given a scenario select appropriate memory RAID and hot spares

1.6 Given a scenario, install appropriate expansion cards into a server while taking fault tolerance into consideration Storage controller [SCSI, SATA, RAID] (SCSI low voltage / high voltage [LVD/HVD], SCSI IDs, Cables and connectors, Active vs. passive termination)

3.1 Describe RAID technologies and its features and benefits Hot spare Software vs. hardware Cache read/write levels (data loss potential) Performance benefits and tradeoffs

3.2 Given a scenario, select the appropriate RAID level 0, 1, 3, 5, 6, 10, 50 Performance benefits and tradeoffs

3.3 Install and configure different internal storage technologies Hot swappable vs. non-hot swappable SCSI, Ultra SCSI, Ultra320 (termination), LUNs SAS, SATA Flash Controller (firmware levels) Hard drive (firmware, JBOD)

6.5 Given a scenario, effectively troubleshoot storage problems, selecting the appropriate tools and methods Storage tools (RAID array management, Array management)

1.4 Installing an NOS

1.4 Explain the importance of a Hardware Compatibility List (HCL) Vendor standards for hardware Memory and processor compatibility Expansion cards compatibility

2.1 Install, deploy, configure and update NOS (Windows / *nix) Installation methods (optical media, USB, network share, PXE) o Imaging system cloning and deployment (Ghost, RIS/WDS, Altiris) Bootloader File systems (FAT, FAT32, NTFS, VMFS, ZFS, EXT3) Driver installation (Driver acquisition, Installation methods, Require media) Configure NOS (Device, OS environmental settings) Patch management

2.4 Explain different server roles, their purpose and how they interact Application server (Update server) Server shut down and start up sequence (one server vs. multiple servers vs. attached components)

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Study Notes Storage and RAID

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Module 1 / Unit 3 Storage and RAID

Objectives

On completion of this unit, you will be able to:

Describe the features and performance characteristics of server-class hard disks and solid state drives.

Describe features of the SCSI interface and know how to configure devices correctly.

Describe features of the SATA and SAS interfaces and know how to configure devices correctly.

Select an appropriate RAID level for a given storage solution.

Configure a RAID array.

Hard Drives

Like a desktop PC, a server will be configured with one or more hard drives to store the operating system and applications software. Disk space may also be provided on a file server as a shared resource for network users.

Unlike most desktop PCs however, server disks will typically be faster for higher performance and add resilience features such as RAID - the ability for multiple hard disks to work together to increase access speed to files or provide redundancy in case one of the drives fails.

All new servers use disk interfaces based on either Serial Attached SCSI (SAS) or Serial Advanced Technology Attachment (SATA). Some older servers may be configured with parallel SCSI interfaces.

Drives are available in two sizes: 3.5" Large Form Factor (LFF) or 2.5" Small Form Factor (SFF). SFF now dominates the market, with LFF drives gradually being phased out.

Delivery Tips

Students should be familiar with basic PC hardware already. Concentrate on SCSI and RAID configuration.

Timings

Theory & Review Questions - 60 minutes

Labs - 30 minutes

Discuss some of the issues in provisioning disks for servers:

* Server role and its effect on disk usage

* Price per gigabyte

* Price per I/O

* Price versus performance requirements

* Tiered storage

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HDDs and SSDs

Most hard disks are of the mechanical type (HDD), where data is stored magnetically on coated metal or glass platters with drive heads to read and write the data. The drive heads must be moved to the required location on the disk, which introduces a degree of latency over and above the time taken for the controller to transfer data, particularly when the data is fragmented across different disk sectors. The performance of a magnetic hard drive is mostly determined by the speed at which the platters are spun (7.2K, 10K, or 15K rpm [revolutions per minute])9.

Recently, flash memory based drives (Solid State Drives [SSD]) have been introduced to the market10. As these have no moving parts, they generally use less power and are lower latency, especially when reading non-sequential data. However, write times can be slower for SSDs than for HDDs. Also, the NAND memory cells used to store data only support a limited number of write/erase cycles, which means that the drive will become less reliable as it ages. To compensate, the OS and the drive controller firmware should perform wear leveling, to distribute writes over different cells.

HP SSD with SATA interface

The advantages and disadvantages of SSDs mean that they are often deployed in servers where there are low disk write requirements. For example, SSDs are better suited to front-end web servers and HDDs to file servers.

9 A 15K drive should support an internal transfer rate of up to about 180 MBps while

7.2K drives will be around 110 MBps. 10

There are broadly two types of SSD: Single Layer Cell (SLC) and Multi Layer Cell (MLC). SLC stores 1 bit per cell while MLC stores 4 or more bits per cell, yielding higher capacities at lower cost. MLC can be slower however as it requires substantial error correction processing. It is also perceived as not reliable enough for enterprise server applications as it supports fewer write cycles, though improvements in the technology may change that perception over time.

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SSDs also carry a significant price premium over HDDs and rise almost exponentially in cost at sizes over 256 GB.

SSDs use the same interfaces as traditional hard drives (that is, SAS or SATA).

Enclosures and Backplanes

A drive is housed in an enclosure or caddy. The drive may then be connected to the controller via a cable but on enterprise-class servers it is more usual for the enclosures to be connected via a backplane. Rather than using cabled connectors, the drives plug (or "mate") into a combined data and power connector on the enclosure. This means that drives can be easily added and removed from the front of the case without having to open the chassis.

Enclosure and backplane on an HP server - 1) The drive mates with the port on the backplane card; 2) Data and power cables on the other side of the backplane card

connect to the drive controller and PSU

The drives are secured and released from the server using a latch. Many server drives are hot-swappable, meaning that they can be added or removed without powering down the server.

1

2

2

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The SCSI Interface

The Small Computer System Interface (SCSI) has been in use as an expansion bus interface since the 1980s. There have been many revisions to the standard. Originally a parallel interface, SCSI is now used for serial connections for disk drives (Serial Attached SCSI) and peripheral devices (Firewire or IEEE1394).

In a PC server, a SCSI adapter (known as the Host Adapter) may be integrated with the motherboard or installed as a PCI-X or PCIe expansion card.

SCSI supports multitasking and multithreading through disconnect-reconnect. When a device experiences a delay in processing a request, it can release control of the bus (disconnect), allowing other devices to use it. When the device is ready to transfer data, it reconnects.

More information about SCSI can be located at the T10 Committee website (www.t10.org) and the SCSI Trade Association (www.scsita.org).

Parallel SCSI Standards

SCSI-1

SCSI-1 is sometimes simply known as SCSI; if a number is not mentioned you can usually assume that SCSI-1 is being referred to. SCSI-1 is defined as an 8-bit bus with a 5 MBps transfer rate. Up to 7 SCSI devices can be daisy-chained to a single SCSI port.

SCSI-1 devices can be used with devices that use the higher transfer rates of the more advanced SCSI-2 protocols, but will cause the whole bus to slow down. Practically speaking therefore, SCSI-1 devices are obsolete.

SCSI-2

The SCSI-2 specification was approved by ANSI in 1990. It is an extensive enhancement of the original standard and defines support for many of the more advanced SCSI features still in use today.

SCSI-2 includes the following enhancements to the original SCSI-1 specification:

Parallel SCSI is obviously diminishing in importance but students still need to know all the configuration issues.

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Type Notes

Fast SCSI A high-speed transfer protocol doubles the speed of the bus to 10 MHz, resulting in a transfer rate of 10 MBps with 8-bit regular SCSI cabling or even higher when used with Wide SCSI (referred to as Fast-Wide SCSI).

Wide SCSI Widening the original 8-bit SCSI bus to 16 bits permits more data throughput at a given signaling speed.

More devices per bus

A bus that runs with Wide SCSI supports 16 devices (including the host adapter).

Improved cables and connectors

SCSI uses a confusingly large number of different cable and connectors. SCSI-2 defines new higher-density connections.

Active termination

Termination is an important technical consideration in setting up a SCSI bus. SCSI-2 defined the use of active termination, which provides more reliable termination of the bus.

Command queuing

One of SCSI's strengths is its ability to allow simultaneous multiple outstanding requests between devices on the bus.

SCSI-3

SCSI-3 is not so much a formal standard as a number of new technologies and sub-standards introduced under the SCSI banner. Some features conflict with each other or represent different approaches to how SCSI is to be implemented or used.

One of the key changes is the use of serial signaling in some products, causing previous versions of SCSI to be retroactively labeled SCSI Parallel Interface (SPI) or "parallel SCSI".

Product Notes

Improved cabling

Improved cabling for the use of Wide SCSI. The use of HVD or LVD signaling and termination allows for greater cable lengths.

Ultra SCSI Doubling the SCSI-2 system bus speed to 20 MHz, meaning 20 MBps with 8-bit SCSI and more with Wide SCSI.

Ultra2 SCSI Another doubling of the system bus speed to 40 MHz. No support for SE signaling.

Ultra3 SCSI Double Data Rate (DDR) signaling, effectively doubling transfer rates, plus improvements to bus communication and arbitration procedures.

Firewire A protocol standard for one type of Serial SCSI used for peripheral device expansion and consumer electronics.

Serial Attached SCSI (SAS)

Serial, point-to-point interface (similar to PCIe) supporting the SCSI command set.

Fiber Channel (FC-AL)

Specification for a Storage Area Network (SAN) architecture supporting the SCSI command set.

iSCSI Use of the SCSI command set over IP-based networks.

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The various "flavors" of Serial SCSI support hot-swapping of devices; some types of parallel SCSI also support hot-swapping.

Summary of SCSI Types

Interface Devices

(Excluding

Host

Adapter)

Rate Max Cable

Length (m)

Connector

SE LVD HVD

SCSI-1 7 5 MBps 6 - 25 50-pin

Fast SCSI

7 10 MBps 3 - 25 50-pin

Fast-Wide SCSI

15 20 MBps 3 - 25 68-pin

Ultra SCSI

7 20 MBps 1.5 - 25 50-pin

Wide Ultra SCSI

15 40 MBps - - 25 68-pin

Ultra2 SCSI

7 40 MBps - 12 25 50-pin

Wide Ultra2 SCSI

15 80 MBps - 12 25 68-pin / 80-pin

Ultra3 SCSI (Ultra160 SCSI)

15 160 MBps - 12 - 68-pin / 80-pin

Ultra320 SCSI

15 320 MBps - 12 - 68-pin / 80-pin

Ultra640 SCSI

15 640 MBps - 12 - 68-pin / 80-pin

Firewire Serial (63 devices)

100 - 800 Mbps

- 4.5 - 6-pin / 9-pin

SAS Serial (128+ devices)

3 - 6 Gbps - 6 - Various

FC-AL Serial (127+ devices)

1 - 4 Gbps - 500+ - Various

The number of devices listed in the table excludes the host adapter. So for example, narrow SCSI supports 8

devices including the host adapter and wide SCSI

supports 16. Note that Firewire, SAS, and Fiber Channel

are serial links and so measured in megabits or gigabits per second rather than megabytes.

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Installing the Host Adapter

The majority of servers will incorporate a SCSI host adapter (most likely to support Serial Attached SCSI) on the motherboard. If SCSI is not supported on the motherboard (or if an upgraded SCSI / RAID solution is required), a host adapter or storage controller must be installed in a suitable expansion slot (typically a x4 or x8 PCIe slot or PCI-X slot).

Remember that SCSI throughput is restricted to the

throughput of the local bus. For example, a host adapter

connected to a version 1 PCIe x1 slot would only have

250 MBps bandwidth and would not be able to take

advantage of Ultra 320 SCSI speeds.

Connecting the SCSI Devices

Parallel SCSI devices may be internal, external or a combination of both. Many configurations are possible. You can connect disk drives, tape devices, CD-ROM drives, and scanners.

Internal devices are connected to a single piece of flat ribbon cable and require a connection to the power supply or (in the case of most drives) plug into a backplane.

External devices are daisy-chained. A cable is connected to the external port at the back of the host adapter, then to one of the two ports at the back of the first external device. If a second device is required, another cable is connected to the first device, then to one of the two ports on the second device and so on. External devices normally require a connection to the mains supply and should be powered up before you turn on the server.

Internal devices - ribbon cable

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External devices - daisy chained

Internal and external devices

SCSI Signaling

In addition to the different parallel SCSI standards, there are three types of parallel SCSI signaling:

Single-Ended (SE - the original specification).

High Voltage Differential (HVD).

Low Voltage Differential (LVD).

Each type places signals on the cabling differently.

SCSI systems use a parallel data path and can suffer from data skew (when the signal on each wire travels at different speeds). This limits cable lengths to 3m (10 feet) for fast SCSI or 6m (20 feet) for standard SCSI using SE signaling.

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Differential SCSI uses two signal paths for each data line and the method by which data is transmitted makes it much less susceptible to corruption. Differential signaling can either be high-power (to achieve longer distances) or low power. In the event, LVD proved much more popular, to the extent that HVD is very rarely found on devices designed for the PC server marketplace.

SE and LVD devices can be combined on the same bus, but the SE maximum bus length then applies and performance of LVD devices can be reduced, as the whole chain operates at the speed of the SE device (unless you use a bus expander connected to the host adapter to separate SE and LVD devices).

HVD devices must not be placed on an SE or LVD bus.

Symbols for SE, HVD, LVD, and LVD/SE (multi-mode) SCSI ports

SCSI Connectors and Cabling

Internal SCSI Connectors

Older internal SCSI devices are generally connected by 50 or 68-way ribbon cable depending on whether the bus is narrow or wide11. The connector on the device is either a male 50-pin IDC (Insulation Displacement Connector)12 or a female 68-pin High Density (HD) connector.

Male and female IDC50 connectors

Male HD68 connector

Most SCSI hard drives now use the Single Connector Attachment (SCA)13. This 80-pin adapter combines the functions of data and power connector and enables autoconfiguration of SCSI settings, such as the ID and termination, and hot-swapping, plus "sideband" signals, such as LED and status monitoring. Such drives slot into a backplane rather than use cabling. The connector on the drive is male.

11

These connectors were also used with backplanes to implement drive arrays. 12

It is possible to obtain 68-wire cable to 50-pin connector adapters. 13

There are two versions: SCA-1 and SCA-2. SCA-1 is obsolete.

Students taking the exam should be aware of the number of pins used in the most common SCSI connectors.

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External SCSI Connectors

External SCSI devices can be connected to the PC-based controller through various types of connector:

SCSI-1 - DB25 or (more commonly) 50-way Centronics "edge" connectors.

Male and female DB25 connectors

Male and female 50-pin Centronics connectors

SCSI-2 and -3 - High Density DB connectors (50-pin and 68-pin) or Very High Density (Micro-Centronics) 68-pin connectors.

High Density 68-pin male and female connectors

Very High Density 68-pin male and female connectors

Centronics connectors use clips to secure the connector; other types are screw-in. The cabling is round and often quite thick because of the heavy shielding used.

Terminating the SCSI Devices

A parallel SCSI bus must be terminated correctly in order to work. Termination absorbs the signal passing along the bus so that it does not reflect back onto the bus and corrupt valid signals.

You must install manual terminators or enable termination on the devices at each end of the SCSI bus. Only SCSI-1 devices require manual termination; the later specifications are self-terminating (automatic termination).

All terminators must be powered. Power can be supplied from the device itself, from the host adapter, or from the backplane (if present).

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Types of Terminator

Different iterations of SCSI have used different termination methods. If all the devices on the bus are the same type, configuration is usually straightforward, but when there is a mix of devices, things can be more complex.

Passive terminators - these are simple devices used with SCSI-1 and SE signaling14. A terminator pack may be internal to the device and enabled or disabled by a jumper or switch or an external resistor pack may need to be fitted.

Active terminators - these contain circuitry to regulate the voltage of the termination current, making them more reliable devices. Active terminators are recommended for SE signaling and required for differential signaling. Active terminators are always built into the device and in many cases will be configured automatically by the SCSI driver software.

Active negation terminators - these contain circuits to cope with fast bus speeds and are required for Ultra SCSI and faster.

Multimode - normally a terminator must match the type of signaling in use, but a multimode (or LVD/SE) terminator is one that can be used with both SE and LVD signaling15. An LED should indicate what type of signaling is in use.

High-byte - if a wide bus contains narrow devices (or a wide device is connected to a narrow bus), the "wide" or "high-byte" signals must be terminated at the point where the bus changes from wide to narrow (typically this will be implemented in the cable adapter).

Enabling and Configuring Terminators

Termination may involve adding a special terminator plug to the open port on the back of the last external device, implementing resistor packs on the device, setting jumpers or switches, crimping a terminator adapter to cabling, or running a setup program. Check your documentation for each device to see how it is terminated.

Host Adapter Termination

The host adapter should be terminated if there are only internal or only external devices attached to it. If both internal and external devices are attached to the host adapter, you should disable termination on the adapter itself and enable termination on the ends of the internal and external chains.

14

A passive terminator is essentially just a resistor; it absorbs the signal. This method is not always completely reliable, especially over longer cable runs. 15

It may also simply be described as providing "LVD Termination"; in which case confirm that it is multimode. You may also see references to "Forced Perfect" terminators; these are used with SE devices to provide better performance than an active terminator.

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Correct termination of a mix of internal and external SCSI device chains

A guide to SCSI configuration can be found at:

www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html

Setting SCSI IDs

A SCSI ID is an identifying label (a number from 0 to 7 [or 0 to 15 for wide SCSI]) assigned to each device. Each device on a SCSI bus must have a unique ID, including the host adapter, which is usually set to 7 or 15. Many older host adapters also insist that the bootable device (usually a hard drive) be set to ID 0.

SCSI IDs are necessary because each device must be uniquely identified when using the SCSI bus or when another device is sending a command. The SCSI ID determines which device has priority. When two or more devices are trying to use the SCSI bus at the same time, the highest ID is given priority (hence the use of 7 for the host adapter).

Make sure your students know how many SCSI devices can be connected together. For example, if 7 devices could be connected to a host adapter (0-6), including the host adapter there are 8 SCSI IDs. Students taking the exam will need to understand this.

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On a wide bus, 7 is still the highest priority ID (it runs 7 to

0 then 15 to 8).

Setting IDs usually involves either physical or software setup. Many external devices have a simple mechanism on the outside for setting the ID, such as a dial or a window displaying the number, and buttons to change it.

Hard drives tend to have their IDs set using jumpers. These jumpers are commonly marked as A0, A1, A2, and A3 on the drive circuit board. The jumpers represent the binary increments 1, 2, 4, and 8 respectively. By combining the jumpers, any ID can be set between 0 and 15.

For example:

Jumper A3 A2 A1 A0

Represents 8 4 2 1

Setting OFF ON OFF ON

Binary digit 0 1 0 1 =5 (SCSI ID5) Setting OFF OFF ON OFF

Binary digit 0 0 1 0 =2 (SCSI ID2)

Plug-and-Play SCSI or SCSI Configured AutoMatically (SCAM) automates the assignment of device IDs and allows the SCSI bus to dynamically shift and reallocate IDs when a new device is added to it. It also allows for the automation (or simplification) of termination.

Logical Unit Number (LUN)

Some parallel SCSI devices can perform more than one function (an auto-loading tape drive for instance). In this case, each function must be allocated a Logical Unit Number (LUN) from 0 to 7 or 0 to 15. This is normally assigned by the manufacturer.

Longer (64-bit) LUNs are also used in Storage Area

Networks (SAN) based on Fiber Channel or iSCSI. See

Unit 2.3 for more information about SANs.

Make sure your students know how to set the SCSI ID with the jumpers.

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SCSI Drivers and Configuration Utilities

When installing a SCSI drive array onto a new computer, the adapter vendor will provide one or more utilities to configure the array. For example, an Adaptec host adapter is provided with the following configuration tools:

Array Configuration Utility / SCSI Select - press CTRL+A when prompted during the boot sequence to use this graphical menu-based program (stored in the adapter's firmware).

Adaptec Storage Manager - boot from the supplied CD / DVD to run this graphical utility.

ARCCONF - a command-line utility that can be used to create batch configuration files.

You can use these tools to configure SCSI bus settings (such as host adapter ID, termination, enable disconnect/reconnect, and so on) and configure a RAID array level (see later in this unit).

With the host adapter installed and the correct SCSI configuration applied, device driver installation for non-hard disk devices can be configured through the operating system or vendor setup utility as normal.

Serial Attached SCSI (SAS)

Serial Attached SCSI is the next generation of SCSI interface. It uses a serial interface with full-duplex communication over 2-pair wiring (much like PCI Express) but retains support for the SCSI command set.

SAS components can be rated at 3 Gbps or 6 Gbps.

A significant feature of SAS is support for thousands of devices (up to 16,384), using an Ethernet switch-like device called an expander. Each device is identified by a unique, manufacturer-coded ID, so there is no manual configuration to be performed. Also, SAS does not require termination, removing another complex configuration issue.

SAS also goes some way to uniting the SATA and SCSI standards. It provides both hardware support (the same connectors and cable) and software support (through the SATA Tunneling Protocol) for SATA drives. This offers the opportunity to mix low-cost SATA drives with high-cost, high-performance SAS drives in an integrated storage solution, providing more flexibility than current models.

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Serial Attached SCSI Connectors

SAS devices feature a combined 7-pin data port16 and 15-pin power port (though some drives may also have a legacy 4-pin Molex power port too).

SAS connections are typically either single-lane (a simple adapter to device connection) or multi-lane (a single port on the adapter is connected to four devices).

Ports can either be "straight-through" or flush / surface mounted with right-angle connectors. Flush-mounted fittings are used in blade servers and other systems with restricted space. SAS backplane connectors are designed to "blind-mate", which means that a connection is made reliably when a drive caddy is inserted into a backplane. The design of the pins also reduces the chance of damage through ESD or a power spike (the full power pins connect after the other pins).

Hot-pluggable drives are not screwed into the chassis but slot into a drive cage. The cables for the devices connect to the drive cage (backplane) rather than the drive units.

Hot-pluggable drives on HP Proliant server

When removing a drive, you will probably need to use a utility or the OS to stop the device. This completes any cached write operations and prevents the NOS from trying to write data to the device while it is being removed. You also need to power down the device, either using software or a switch on the drive bay. Indicators on the drive bay should show when a drive is safe to remove. The drives are physically released and inserted using a lever or latch mechanism.

Unused drive slots should be filled with blanks to maintain

the correct airflow and cooling within the chassis.

A number of connectors are associated with the use of SAS host adapters and drives:

16

In fact, on most SAS devices there are two data connectors (for redundancy). This is referred to as "dual-port". Obviously the backplane or cable must also support a redundant connection for this to work.

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SFF 8087 - internal mini connector for both adapter card ("host") and 4 drive or backplane ports ("target").

SFF 8088 - external mini connector for both adapter card and drive enclosures.

8087 and 8088 are newer connectors (with the product

name Molex iPass) and will support increased SAS bus

speeds when standardized (rated up to 10G).

SFF 8484 ("Multilane") - legacy 32-pin internal or external HD connector (host) supporting four 7-pin lanes (target). The remaining pins are used for "sideband" signals (LEDs and status monitoring).

SFF 8470 ("Infiniband") - legacy jackscrew connector for both internal and external use.

SFF 8482 - internal connector compatible with both SAS and SATA drives. This type of connector would be used principally to attach SATA devices (such as DVD drives) to an SAS bus.

The Serial ATA Interface

Serial ATA (SATA) was developed to address the limitations of the now obsolete parallel ATA or IDE interface. SATA would be used on low-end server hardware as a cheaper option than SAS.

4 SATA motherboard ports in front of an IDE port on an Intel motherboard

As the name suggests, SATA transfers data in serial format. This allows for thinner, longer, more flexible cables (up to 1m [39"]) with smaller, 7-pin data connectors. Each port supports a single device.

SATA cable for HP workstations

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The original SATA standard (SATA 1.5 Gbit/s or SATA/150) supports speeds of up to 150 MBps. This standard was quickly augmented by SATA 2.0, which specifies a 3 Gbps (300 MBps) transfer rate, and then SATA 3.0, running at 6 Gbps.

Other additions in SATA 2.0 include the use of port multipliers, which allow up to 15 drives to be connected to a single SATA adapter, and Native Command Queuing (NCQ), which enables the drive to analyze read/write operations and perform them in the most efficient manner, depending on the location of data on the disk

SATA 6 Gbps adds some extensions to NCQ to support isochronous data transfer (prioritizing real time data such as video to ensure smooth playback).

There is also an eSATA standard for the attachment of external drives, with a 2m (78") cable. The main drawback of eSATA compared to USB or Firewire external drives is that power is not supplied over the cable. This is not so much of an issue for 3.5" drives, which require a separate power supply anyway, but limits the usefulness of eSATA for 2.5" portable drives. This drawback is addressed by the eSATAp standard, which uses a different port and connector to eSATA.

More information on SATA standards can be obtained from www.sata-io.org.

Hot Swapping

One of the major advantages of SATA over PATA is the support for hot swapping and consequently better compatibility with RAID configurations. Serial ATA 15-pin power connectors have been redesigned to provide support for both hot plugging and a 3.3V power supply in addition to the usual 5V and 12V.

Many drives retain a 4-pin Molex port for compatibility with legacy power supplies). Molex-SATA conversion adapters are also available.

SATA power connector

SATA and SAS

As mentioned earlier, SAS includes hardware and software support for SATA devices. The reverse is not true however; SAS devices cannot be plugged into an SATA bus.

A single enclosure could contain a mix of SAS and SATA devices, though a mix of SATA and SAS could not be used in the same logical volume. Mixing 3 Gbps and 6 Gbps devices is generally not recommended as it may impair 6 Gbps operation.

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Drive Arrays (RAID)

With RAID (Redundant Array of Independent Disks), multiple physical disks can be grouped into a single logical volume. Usually, this is done to improve fault tolerance; if a physical drive fails, the logical volume is protected by the data stored on the other physical drives in the array.

RAID can also be said to stand for "Redundant Array of

Inexpensive Disks" and the "D" can also stand for

"devices".

The RAID advisory board defines RAID levels. The most common levels are numbered from 0 to 6, where each level corresponds to a specific type of fault tolerance. There are also proprietary RAID solutions.

RAID Level Fault Tolerance

Level 0 Striping without parity (no fault tolerance) Level 1 Mirroring/duplexing Level 2 Striping with ECC (Error Correction Code) Level 3 Striping with a dedicated parity disk Level 4 Independent data disks with shared parity disk Level 5 Independent data disks with distributed parity

blocks (striping with parity) Level 6 Second parity

In addition to these primary levels, it is also possible to "nest" one RAID solution within another (for example, you could mirror two stripe sets to boost performance without sacrificing fault tolerance).

RAID Performance

To choose an optimum RAID solution, you need to balance the server role with factors such as cost, performance, and security. Higher RAID levels usually require more costly controllers. Security is a measure of the number of drive failures that an array can support.

Performance involves a number of different factors but the most important to assess are probably the balance between read and write operations and between transactional and sequential Input / Output (I/O):

RAID is heavily tested on the exam, so make sure students understand different RAID levels, calculating usable storage, number of failures a configuration can support, hardware versus software implementations, and options for reconfiguring an existing array.

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Read / write balance - depending on the server role, disk activity may be predominantly reads or writes (for example, 80% reads and 20% writes). Some RAID levels have better read performance and some have better write performance.

Sequential versus transactional (or random) I/O - this refers to how data on the volume is typically accessed. Sequential I/O means reading or writing data at the same physical location; transactional (or random) I/O means the controller has to scan different areas of the disk or array to retrieve or write the data. In terms of database applications, transactional I/O is associated with adding and updating records while sequential I/O is more typical of querying data for reports or serving large files. The OS and user file access is also typically transactional but a media server would use predominantly sequential I/O.

RAID 0 (Striping Without Parity)

Disk striping is a technique where data is divided into blocks and spread in a fixed order among all the disks in the array. The block stripe size is often 64K but can be configured to an optimum value between 2K and 512K based on the size of the array and the type of data served (in much the same way as a cluster size can be chosen for a volume file system).

Data7Data6Data4Data1

Data8Data5Data3Data2

RAID 0 (striping) - data is spread across the array

RAID 0 requires at least two disks. Its principal advantage is to improve performance by spreading disk I/O over multiple drives. As disk reads and writes can take place on multiple disks simultaneously, the effect of latency (the time taken for the disk head to locate a sector on the disk) is reduced. The number of physical disks used in the array sets the stripe width; using more disks (greater width) should benefit performance. Also, the best performance is obtained when each disk has its own controller.

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The logical volume size is the combined total of the smallest capacity physical disk in the array. When building a RAID array, all the disks should normally be identical in terms of capacity17. If disks are different size, the size of the smallest disk in the array determines the maximum amount of space that can be used on the larger drives. RAID 0 adds no storage overhead and is a means of obtaining a large logical volume from multiple, low capacity disks.

However, because it provides no redundancy, this method cannot be said to be a true RAID implementation. If any physical disk in the array fails, the whole logical volume will fail, causing the server to crash and requiring data to be recovered using disk recovery tools (and as the data on the failed physical disk may not be recoverable, this can be very difficult, if not impossible). Note that the chance of failure increases with the number of drives used in the array (stripe width).

Consequently, RAID 0 would never be used for live data storage. It has specialist applications for hosting read-only or relatively static data18 (in a front-end web server or media server to serve files that are backed up elsewhere for instance) where speed is more important than data security.

As well as data security, RAID 0 risks availability, as the

failure of one disk causes the whole array, and therefore

the server, to fail. You could compensate for this by

duplicating servers (clustering) but only at considerable

expense.

RAID 1 (Mirroring/Duplexing)

Mirroring requires two hard disks19 and a single disk controller. The mirror disk is a duplicate of the data disk. Each write operation is duplicated on the second disk in the set, introducing a small performance overhead. A read operation can use either disk, boosting performance somewhat.

Performance is difficult to quantify but RAID 1 is generally

seen as performing worse than a single drive but better

than higher RAID levels at writes and better than a single

drive but worse than other RAID levels at reads.

17

And ideally in terms of type and performance, though this is not mandatory. 18

That is, if it is acceptable to rely upon the last backup made for data recovery. 19

It is possible, in some implementations, to add more mirrors (triple-mirrored RAID). Storage efficiency is very low though.

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This strategy is the simplest way of protecting a single disk against failure. If one disk fails (degrading the array), the other takes over. There is little impact on performance during this time (obviously the boost of having two drives available for read operations is lost), so availability remains good, but the failed disk should be replaced as quickly as possible as there is no longer any redundancy. When the disk is replaced, it must be populated with data from the other disk (rebuilding). Performance while rebuilding is reduced, though RAID 1 is better than other levels in that respect and the rebuilding process is generally shorter than parity-based RAID.

Data123

Data123

RAID 1 (Mirroring) - data is written to both disks simultaneously

In terms of cost per gigabyte, disk mirroring is more expensive than other forms of fault tolerance because disk space utilization is only 50 percent. Also the total volume size cannot exceed the available capacity of the physical disks. However, for peer-to-peer and modest server-based LANs or for enterprise workstations, disk mirroring usually has a lower entry cost because it requires only two disks and a relatively cheap RAID controller. Stripe sets with parity (RAID level 5) require three or more disks and the RAID controllers are more expensive. RAID 1 is also a good choice for servers where fault tolerant write performance is paramount.

Duplexing is simply a mirrored pair with an additional disk controller on the second drive. This reduces channel traffic and potentially improves performance. Duplexing is intended to protect against controller failures as well as media failures.

Data123

Data123

RAID 1 (Duplex mirror) - an extra controller provides redundancy

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RAID 3 (Striping with Parity Disk)

RAID 320 uses byte-level striping with a dedicated parity disk. Parity is extra information recorded by the array so that if one of the disks fails, the data can be reconstructed from the parity information until a replacement disk can be added. RAID 3 requires 3 disks - two for the stripe set and one for the parity information. It can support the failure of any one of the three disks and performance is not substantially impaired when the array is degraded. The parity calculations mean that rebuilding the array can take a long time however.

The use of small byte-level stripe sizes means good performance with large files and other types of sequential I/O (such as streaming media files) but poor performance with random access (especially random write access). The use of a dedicated parity disk can also impair write performance, as the disk is a bottleneck under heavy loads.

RAID 4 also uses a dedicated parity disk but uses block-level striping rather than byte-level striping. As such, it offers almost no advantages compared to RAID 5 (see below) and consequently is not widely used.

RAID 5 (Striping with Distributed Parity)

Striping with parity (RAID 5) is a popular strategy for fault tolerant designs. It differs from RAID 3 in that it writes parity information across all the disks in the array. The data and parity information are managed so that the two are always on different disks. If a single disk fails, enough information is spread across the remaining disks to allow the data to be completely reconstructed. Only one disk failure can be tolerated however and performance while the array is degraded can be poor. Rebuilding is also lengthy.

Read performance is good, especially for transactional (or random) I/O. Write performance is better than RAID 3 but worse than RAID 1.

20

RAID 2 was never developed into a commercial product.

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Data7Parity5-6

Data3Data1

Data8Data5

Parity3-4

Data2

Parity7-8

Data6Data4

Parity1-2

RAID 5 (Striping with Parity)

RAID 5 requires a minimum of three drives but can be configured with more. This allows more flexibility in determining the overall capacity of the array than is possible with RAID 1. A "hard" maximum number of devices is set by the controller or OS support but the number of drives used is more likely to be determined by practicalities such as cost and risk (remember that adding more disks increases the chance of failure).

If the controller supports it, the risk of disk failure can be

offset by configuring a hot spare (see "Enterprise RAID

Configurations") below.

RAID 6 (Second Parity)

RAID 6 is like RAID 5 but with two sets of parity information, meaning that the array can support the simultaneous loss of two disks before it fails. This improves fault tolerance and availability at the expense of write performance. Rebuilding the array is still slow but the backup of a second parity set means that the operation can be delayed more safely to a convenient time than is the case with RAID 5. RAID 6 requires a minimum of 4 disks.

RAID 6 is not that widely deployed however as RAID 5 with a hot spare or nested RAID are generally seen as providing more effective solutions.

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Nested RAID

Nested RAID means configuring an array of arrays (or a spanned array) to combine the benefits of redundancy and performance. Nested RAID also allows for larger logical volumes while preserving fault tolerance. The main drawbacks are that these solutions tend to use a lot of disk units and require more expensive RAID controllers.

RAID 0+1 / RAID 1+0 (RAID 10)

As described above, RAID 0 is striping with no parity (that is, no fault tolerance is provided). This provides high throughput, but leaves the data at risk. RAID 1 provides mirroring; the highest achievable disk fault tolerance. RAID 0+1 is a combination of both these configurations. Two stripes sets with no parity are mirrored, thus providing fault tolerance.

This configuration provides for very high throughput and can support one disk failure in the array. Note that it carries the same 50% disk overhead that mirroring does.

You will need at least four disks to create this configuration and there must be an even number of disks.

RAID 1+0 (or RAID 10) is a stripe of mirrors. This configuration offers better fault tolerance (one disk in each mirror can fail and the array will still function) and consequently is more popular than RAID 0+1. Sometimes though, the terms are used interchangeably by vendors.

Volume (RAID 0)

Sub-volume (RAID 1)

Data7Data5Data3

Data1

Data7Data5Data3

Data1

Data8Data6Data4

Data2

Data8Data6Data4

Data2

Sub-volume (RAID 1)

RAID 10 - either disk in each of the sub-volumes can fail without bringing down the

main volume

RAID 10 allows for large logical volumes (an array may support up to 128 disks for instance) and high performance. The main drawbacks are the 50% disk space utilization and the need for a costly RAID controller.

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RAID 5+0 (RAID 50)

RAID 5 provides for fault tolerance across a stripe set. It allows for moderate write performance, good read performance, and acceptable fault tolerance. RAID 0 gives higher throughput but no fault tolerance.

RAID 5+0 (or RAID 50) is RAID 5 sets striped across a RAID 0 set. This provides better performance and fault tolerance. Each of the RAID 5 stripes can sustain a single disk failure, so in essence, your single RAID 5+0 array can support multiple disk failures.

Volume (RAID 0)

Sub-volume (RAID 5)

Data7

Parity5-6

Data3

Data1

Data8

Data5

Parity3-4

Data2

Parity7-8

Data6

Data4

Parity1-2

Sub-volume (RAID 5)

Data15

Parity13-14

Data11

Data9

Data16

Data13

Parity11-12

Data10

Parity15-16

Data14

Data12

Parity9-10

Sub-volume (RAID 5)

Data23

Parity21-22

Data19

Data17

Data24

Data21

Parity19-20

Data18

Parity23-24

Data22

Data20

Parity17-18

RAID 50 - data is striped (RAID 0) across three RAID 5 subvolumes of three disks

each; one disk in each subvolume can fail without data loss

A minimum of six disks is required, the number of disks must have factors that are two integers (for example, RAID 5+0 could use 10 disks but not 11), and one integer must be 2 or greater and the other integer 3 or greater. The configuration of the array determines fault tolerance and capacity. For example, an array with 2 sets of 6 disks has better storage efficiency but worse fault tolerance than an array of 4 sets of 3 disks.

The main advantage of RAID 5+0 is the support for very large fault tolerant volumes with better storage efficiency than RAID 1+0. The main disadvantage is that the controllers that can support RAID 5+0 are at the top end of the market and consequently very costly. Write performance will generally be lower than RAID 1+0 but read performance (especially random reads) will be better.

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RAID 5+1

RAID 5+1 (or RAID 51) is mirroring RAID 5 arrays. This provides outstanding fault tolerance and availability, but is complex to implement and expensive; as well as the cost of the controller, the array is likely to have below 50% storage efficiency.

Calculating Usable Storage

The following table shows how to calculate the amount of disk space available when using commonly implemented RAID configurations.

If the disks are different sizes, the size used is that of the

smallest disk. Extra disk space on larger drives is wasted.

RAID Level Usable Disk Space

Level 0 Total space of all disks in stripe set. For example, 3 disks each 80 GB in size would result in a 240 GB volume.

Level 1 Half of the disk space on the disks is available. One disk is a copy of the other. Therefore, if you implement RAID 1 with two 80 GB disks, you end up with 80 GB of storage available.

Level 3 Level 4

One disk is used for parity so the total available space is the capacity of all the drives but one.

Level 5 Level 6

(# Drives - 1) * Drive Size for RAID 5 or (# Drives - 2) * Drive Size for RAID 6. The level of fault tolerance and available disk space are inverse. As you add disks to the set, fault tolerance decreases but usable disk space increases21. If you configure a RAID 5 set using 3 disks, of each disk is set aside for parity; if four are used, is reserved on each disk. Using a three 80 GB disk configuration would create a 160 GB usable volume.

Level 0+1 Level 1+0

This is the same as for RAID 1: (Drive Size * # Drives) / 2 (or half)

Level 5+0 The array capacity is: Drive Size * (# Drives per Set -1) * # Sets. The storage efficiency is: (# Drives per Set -1) / # Drives per Set For example, in an array of 12x80 GB disks, a 2x6-disk array gives a capacity of 800 GB (80*(6-1)*2) - 83% efficiency. A 3x4-disk array has a capacity of 720 GB - 75% efficiency.

21

Remember that a RAID 5 array can only sustain a single drive failure; RAID 6 can sustain two drive failures. The more drives there are in a set, the higher the risk is that one will fail.

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Implementing RAID

It is possible to implement RAID using either hardware or software.

Hardware Solutions

A hardware solution means that creating volumes from an array of physical disks is an operation supported by a plug-in controller card or by the motherboard22, independently of the installed operating system. Hardware solutions are principally differentiated by their support for RAID levels. Entry-level controllers might support only RAID 0 or RAID 1, mid-level controllers might add support for RAID 5, RAID 6, and RAID 1+0, while the top-end would add support for RAID 5+0 and RAID 5+1. Vendors may also define proprietary RAID levels and solutions.

In addition, some hardware implementations allow you to replace a failed drive without shutting down the system. Another advantage of hardware-based RAID is that the operating system sees the array as one volume. This allows you to install the operating system onto an array, which isn't always possible when using software arrays. The disadvantages of a hardware implementation are that they can be more expensive than software solutions and may lock you into a single vendor solution.

A RAID controller may have the following performance-boosting components:

Processor - a true RAID controller card comes with a CPU to han

comptia server plus courseware instructor sample

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