ASM 11g R1/R2 Enhancements

Suresh Gandhi

Agenda

R1 Enhancements– New Disk Group Compatibility Attributes – Fast Mirror Resync – Rolling Upgrade – SYSASM Privilege and OSASM OS Group – Scalability and Performance Enhancements – New ASMCMD Commands and Options – Preferred Read Failure Groups – Fast Rebalance – Miscellaneous Disk Group Maintenance Enhancements

R2 Enhancements– ASM Cluster File System (ACFS)– ASM Dynamic Volume Manager (ADVM)– ASM FS Snapshot– Oracle Cluster registry OCR and Voting Disk on ASM– ASM Intelligent Data Placement– ASM Storage Management Configuration Assitant– ASM File Access Control

Some Practices on new – Database Home on ACFS Filesystem– Invoking ASMCMD Commands for volume management

ASM How it works

Server RDBMS ASM

Disk Group

Create File

Allocation

File

I/OExtent Map

OS / ADVM

- File Layout Info

- Update Statistics

- Health Info

Database File Open

ASM Manages Metadata

Not in I/O Path

RAW Performance

Disk Group

Some Important Notes on ASM: Oracle ASM Storage Limits

– Oracle ASM provides near unlimited capacity for future growth, but does have some storage limits. For example, Oracle ASM has the following limits on the number of disk groups, disks, and files: 63 disk groups in a storage system 10,000 Oracle ASM disks in a storage system 1 million files for each disk group

Without any Oracle Exadata Storage, Oracle ASM has these storage limits: 2 terabytes (TB) maximum storage for each Oracle ASM disk 20 petabytes (PB) maximum for the storage system

With all Oracle Exadata Storage, Oracle ASM has these storage limits: 4 PB maximum storage for each Oracle ASM disk 40 exabytes (EB) maximum for the storage system

The maximum size limit of a disk group equals the maximum disk size multiplied by the maximum number of disks in a disk group (10,000).

File size limits are dependent on the value of the disk group compatibility attributes. Oracle ASM supports file sizes greater than 128 TB in any redundancy mode when the COMPATIBLE.RDBMS disk group attribute is set greater than10.1.

If COMPATIBLE.RDBMS is set to 10.1, the file size limits are less. For example, with COMPATIBLE.RDBMS equal to 10.1 and the AU size equal to 1 MB, Oracle ASM file size limits are:

External redundancy: 35 TB Normal redundancy: 5.8 TB

– High redundancy: 3.9 TB

R1 – New Disk Group Compatibility Attributes

Oracle 11g ASM includes two new compatibility attributes that determine the version of the ASM and database software that can use specific disk groups:

COMPATIBLE.ASM - The minimum version of the ASM software that can access the disk group. In 11g, the default setting is 10.1.

COMPATIBLE.RDBMS - The minimum COMPATIBLE database initialization parameter setting for any database instance that uses the disk group. In 11g, the default setting is 10.1.

SQL> CREATE DISKGROUP data DISK '/dev/raw/*' ATTRIBUTE 'compatible.asm' = '11.1';

SQL> CREATE DISKGROUP data DISK '/dev/raw/*' ATTRIBUTE 'compatible.rdbms' = '11.1', 'compatible.asm' = '11.1';

Note:- The compatibility versions of a disk group can only be increased, not decreased. If you have increased the version by mistake, you will need to create a new disk group.

SELECT group_number, name, compatibility, database_compatibility FROM v$asm_diskgroup;

GROUP_NUM# NAME COMPATIBILITY DATABASE_COMPATIBILI------------ ---------- -------------------- -------------------- 1 DATA 11.1.0.0.0 11.1.0.0.0

R1 - Fast Mirror Resync

During transient disk failures within a failure group, ASM keeps track of the changed extents that need to be applied to the offline disk. Once the disk is available, only the changed extents are written to resynchronize the disk, rather than overwriting the contents of the entire disk. This can speed up the resynchronization process considerably.

Applicable only when Disk Compatable Attribute set to 11.1.0 or higher

Default time to repair the disk is 3.6 hrs determine by DISK_REPAIR_TIME attribute

Can override by using Alter disk offline disk clause.

R1 - Scalability and Performance Enhancements

ASM files are stored in a disk group as a collection of extents Oracle 10g each extent mapped directly to one allocation unit (AU) In 11G,

– an extent can be made up of one or more allocation units – As files get larger, the extent size can grow to reduce the size of the

extent map describing the file– When the disk group compatibility attributes are set to 11.1 or higher,

The first 20,000 extents match the allocation unit size (1*AU) The next 20,000 extents are made up of 8 allocation units (8*AU). Beyond that point, the extent size becomes 64 allocation units (64*AU).

Also controls or enhances the AU size by specifying 'au_size' disk attribute

CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1' ATRRIBUTE 'au_size' = '32M';

Values can be ranging from 1M to 64M

R1 - Preferred Read Failure Groups

In Oracle 10g, ASM always reads the primary copy of the mirrored extent set.

This isn't a problem when both nodes and both failure groups are all located in the same site, but it can be inefficient for extended clusters, causing needless network traffic.

Oracle 11g allows each node to define a preferred failure group, allowing nodes in extended clusters to access local failure groups in preference to remote ones

Instance Level Parameter ASM_PREFERRED_READ_FAILURE_GROUPS must be set for each node

Example:-

SQL> ALTER SYSTEM SET ASM_PREFERRED_READ_FAILURE_GROUPS = 'data.data_0000', 'data.data_0001', 'data.data_0002';

R1 - Fast Rebalance

The "ALTER DISKGROUP ... MOUNT" statement allows disk groups to be mounted in restricted mode.

Using RESTRICTED mode improves the performance of rebalance operations in a RAC environment as it elimitates the need for lock and unlock extent map messaging that occurs between ASM instances

SQL> SELECT name FROM v$asm_diskgroup;

NAME------------------------------DATA

SQL> ALTER DISKGROUP data DISMOUNT;

Diskgroup altered.

SQL> ALTER DISKGROUP data MOUNT RESTRICTED;

Diskgroup altered.

SQL> ALTER DISKGROUP data DISMOUNT;

Diskgroup altered.

SQL> ALTER DISKGROUP data MOUNT;

Diskgroup altered.

R1 - Disk Group Maintenance Enhancements

The CHECK clause of the ALTER DISKGROUP command has been simplified so there are only two options, NOREPAIR and REPAIR, available, with NOREPAIR as the default. Summarized errors are displayed, with full error messages writen to the alert log.

– ALTER DISKGROUP data CHECK; -- Like NOREPAIR– ALTER DISKGROUP data CHECK NOREPAIR;– ALTER DISKGROUP data CHECK REPAIR;

The ALTER DISKGOUP command now includes ONLINE and OFFLINE clauses so disks can be taken offline for repair before being brought back online.

– -- Individual disks. ALTER DISKGROUP data OFFLINE DISK 'disk_0000', 'disk_0001'; ALTER DISKGROUP data ONLINE DISK 'disk_0000', 'disk_0001';

– -- Failure groups. ALTER DISKGROUP data OFFLINE DISKS IN FAILGROUP 'fg_0000'; ALTER DISKGROUP data ONLINE DISKS IN FAILGROUP 'fg_0000';

– -- Bring online all disks in disk group. ALTER DISKGROUP data ONLINE ALL;

Disk groups that can't be mounted by ASM can now be dropped using the FORCE keyword of the DROP DISKGROUP command.

DROP DISKGROUP data FORCE;

R1-ASMCMD new commands

Md_backup:- MD_Restore CP Startup remap

ASM – Extending to Manage ALL DATA

R2 - ASM Dynamic Volume Manager (ADVM)

The ASM Dynamic Volume Manager (DVM) is a kernel-loadable device driver that provides a standard device driver interface to clients (for example, ACFS).

The ASM Dynamic Volume Manager (DVM) provides a standard I/O interface allowing general purpose file systems to leverage the full functionality of ASM as a volume manager

Oracle database files as well as non-Oracle database files, for example Oracle binaries, can now reside on ACFS eliminating the need for third-party file systems or volume managers to host general purpose files.

R2 – ASM Cluster File System

a robust, modern, general purpose file system for files beyond the Oracle database files.

ACFS provides support for files such as Oracle binaries, report files, trace files, alert logs, and other application data files.

ACFS is highly available leveraging the ASM mirroring and striping features in addition to hardware Redundant Array of Inexpensive Disks (RAID) functionality.

ACFS supports large files with 64-bit file and file system data structure sizes leading to exabyte-capable file and file system capacities

R2 – ASM Snapshots

ASM FS Snapshot is a point-in-time copy of a file system and can provide up to 64 snapshot images. ASM FS Snapshot performs fast creation of persistent ASM FS images at a specific point-in-time with low overhead leveraging the Copy on Write technology.

Read-only ASM FS Snapshots can be generated on an interval basis. They may reside in existing ASM FS storage or in an additional storage device and persist following a system restart.

Even as the file system changes, the snapshot does not, giving you the ability to view the file system as it was at the time the snapshot was created. Initially, snapshots are read-only, which preserves their point-in-time capture. The following are the benefits of ASM FS Snapshots:

– ASM FS Snapshots can be used as a source for backup. The original file system can continue to change but the static nature of the snapshot makes them ideal as a source for backup without keeping the original file system offline.

– ASM FS Snapshots can be used as a means for you to recover accidentally deleted or modified files.

– ASM FS Snapshots can be used as a source for data mining or report applications which need to work on a static, point-in-time data set.

R2 – Cluster Registry (OCR)/Voting Disk on ASM

Automatic Storage Management (ASM) disks are used to store the Oracle Cluster Registry (OCR) and the voting disks. ASM Partnership and Status Table (PST) is replicated on multiple disks and is extended to store the OCR. Consequently, the OCR tolerates loss of the same number of disks as the underlying disk group. OCR is relocated in response to disk failures.

ASM reserves a number of blocks at a fixed location of every ASM disk for storing the voting disk. Should the disk holding the voting disk fail, ASM selects another disk to store this data.

Storing the OCR and the voting disk on ASM eliminates the need to use expensive third-party cluster volume managers or deal with the complexity of managing disk partitions for OCR and voting disks in Oracle RAC configurations.

Create DISKGROUP contains the option for REGULAR or QUORUM Disks The FAILGROUP_TYPE column in both the V$ASM_DISK and

V$ASM_DISK_STAT views specifies failure group type. The value for this column is REGULAR for regular failure groups and QUORUM for quorum failure groups.

R2 – Intelligent Data Placement

Disk drives have higher transfer rates and bytes per track on the outer tracks. This makes it preferable to keep the hotter data closer to the edge of the disk; that is, the lower numbered blocks.

This feature enables ASM to identify higher performance disk regions. Most frequently accessed ASM files can be marked to be moved into the hot region and take advantage of higher I/O performance (for example, hot tablespaces and indices) and able to better meet the application I/O demand.

This feature is only applicable when whole physical disks are presented to ASM versus local unit numbers (LUN).

Most frequently accessed Oracle database files in ASM disk groups (ASM files) can be placed in hot disk regions to deliver higher bandwidth and reduce seek latency to meet the application I/O performance requirements.

Examples:-

Volume– Ex:- volcreate –G Test -s 10G –primary hot/cold TEST_VOL

Diskgroup– Ex:-alter diskgroup data add template hotfiles attributes (hot mirrorhot);

Files– Ex:- ALTER DISKGROUP ASMDISK01 MODIFY FILE '+ASMDISK01/BDBE01/DATAFILE/APP_DATA.256.697380955'

ATTRIBUTES (HOT)

Practices/References

Practice view

ASMCMD references with releases

ASM_Practice

asmcmd_reference

References:-

Most useful information querying V$ views for ASM– http://database.in2p3.fr/doc/oracle/Oracle_Database_11_Release_1_(11.

2)_Documentation/server.112/e10500/asmviews.htm

Storage Administrator Guide

http://database.in2p3.fr/doc/oracle/Oracle_Database_11_Release_1_(11.2)_Documentation/server.112/e10500/asmviews.htm

Best book on ASM

Oracle Automatic Storage Management: Under-the-Hood & Practical Deployment Guide by Nitin Vengurlekar, Murali Vallath, Rich Long itin Vengulerkar – ASM

Q & A