Disk Group Attributes

Disk Group Attributes

Disk group attributes are parameters that are bound to a disk group, rather than an Oracle ASM instance.
Disk group attributes can be set when a disk group is created or altered, unless otherwise noted in the following list.
ACCESS_CONTROL.ENABLED
This attribute can only be set when altering a disk group.
This attribute determines whether Oracle ASM File Access Control is enabled for a disk group.
The value can be true or false. The default is false.
If the attribute is set to true, accessing Oracle ASM files is subject to access control. If false, any user can access every file in the disk group. All other operations behave independently of this attribute.
ACCESS_CONTROL.UMASK
This attribute can only be set when altering a disk group.
This attribute determines which permissions are masked out on the creation of an Oracle ASM file for the user that owns the file, users in the same user group, and others not in the user group. This attribute applies to all files on a disk group.
The values can be combinations of three digits {0|2|6} {0|2|6} {0|2|6}. The default is 066.
Setting to 0 masks out nothing. Setting to 2 masks out write permission. Setting to 6 masks out both read and write permissions.
Before setting the ACCESS_CONTROL.UMASK disk group attribute, you must set the ACCESS_CONTROL.ENABLED attribute to true to enable Oracle ASM File Access Control.

Setting up Oracle ASM File Access Control

ALTER DISKGROUP data1 SET ATTRIBUTE 'access_control.enabled' = 'true';

ALTER DISKGROUP data1 SET ATTRIBUTE 'access_control.umask' = '026';

AU_SIZE
This attribute can only be set when creating a disk group.
Oracle recommends that the allocation unit (AU) size for a disk group be set to 4 megabytes (MB). In addition to this AU size recommendation, the operating system (OS) I/O size should be set to the largest possible size.
Some benefits of a 4 MB allocation unit are:

·         Increased I/O through the I/O subsystem if the I/O size is increased to the AU size.

·         Reduced SGA size to manage the extent maps in the database instance.

·         Faster datafile initialization if the I/O size is increased to the AU size.

·         Increased file size limits.

·         Reduced database open time.

The allocation unit size is specified with the disk group attribute AU_SIZE. The AU size cannot be altered after a disk group is created. Example 4-1 shows how the AU_SIZE is specified with the CREATE DISKGROUP SQL statement.

Example 4-1 Creating the DATA disk group

CREATE DISKGROUP data NORMAL REDUNDANCY

  FAILGROUP controller1 DISK

    '/devices/diska1' NAME diska1,

    '/devices/diska2' NAME diska2,

    '/devices/diska3' NAME diska3,

    '/devices/diska4' NAME diska4

  FAILGROUP controller2 DISK

    '/devices/diskb1' NAME diskb1,

    '/devices/diskb2' NAME diskb2,

    '/devices/diskb3' NAME diskb3,

    '/devices/diskb4' NAME diskb4

  ATTRIBUTE 'au_size'='4M',

    'compatible.asm' = '11.2', 

    'compatible.rdbms' = '11.2',

    'compatible.advm' = '11.2';

In Example 4-1, the NAME clauses enable you to explicitly assign names to the disks rather than the default system-generated names. The system-generated names are in the form diskgroup_nnnn, where nnnn is the disk number for the disk in the disk group. For ASMLib disks, the disk name defaults to the ASMLib name that is the user label of the disk; for example, mydisk is the default Oracle ASM disk name for ORCL:mydisk.
When creating the disk group in Example 4-1, the values of following disk group attributes were explicitly set:

·         AU_SIZE

Specifies the size of the allocation unit for the disk group. For information about allocation unit size and extents, see "Extents".

You can view the value of the AU_SIZE disk group attribute in the ALLOCATION_UNIT_SIZE column of the V$ASM_DISKGROUP view.

·         COMPATIBLE.ASM

Determines the minimum software version for any Oracle ASM instance that uses a disk group. For information about the COMPATIBLE.ASM attribute, see "COMPATIBLE.ASM".

·         COMPATIBLE.RDBMS

Determines the minimum software version for any database instance that uses a disk group. For information about the COMPATIBLE.RDBMS attribute, see "COMPATIBLE.RDBMS".

·         COMPATIBLE.ADVM

Determines whether the disk group can contain Oracle ASM volumes.

CELL.SMART_SCAN_CAPABLE
This attribute is only applicable to Oracle Exadata storage.

COMPATIBLE.ASM

The value for the disk group COMPATIBLE.ASM attribute determines the minimum software version for an Oracle ASM instance that can use the disk group. This setting also affects the format of the data structures for the Oracle ASM metadata on the disk. The format of other file contents is determined by Oracle ASM Dynamic Volume Manager (Oracle ADVM) and the database instance.
For Oracle ASM in Oracle Database 11g, 10.1 is the default setting for the COMPATIBLE.ASM attribute when using the SQL CREATE DISKGROUP statement, the ASMCMD mkdg command, and Oracle Enterprise Manager Create Disk Group page. When creating a disk group with ASMCA, the default setting is 11.2.

COMPATIBLE.RDBMS

The value for the disk group COMPATIBLE.RDBMS attribute determines the minimum COMPATIBLE database initialization parameter setting for any database instance that is allowed to use the disk group. Before advancing the COMPATIBLE.RDBMS attribute, ensure that the values for the COMPATIBLE initialization parameter for all of the databases that access the disk group are set to at least the value of the new setting for COMPATIBLE.RDBMS.
For example, if the COMPATIBLE initialization parameters of the databases are set to either 11.1 or 11.2, then COMPATIBLE.RDBMS can be set to any value between 10.1 and 11.1 inclusively.
For Oracle ASM in Oracle Database 11g, 10.1 is the default setting for the COMPATIBLE.RDBMS attribute when using the SQL CREATE DISKGROUP statement, the ASMCMD mkdg command, ASMCA Create Disk Group page, and Oracle Enterprise Manager Create Disk Group page.

COMPATIBLE.ADVM

The value for the disk group COMPATIBLE.ADVM attribute determines whether the disk group can contain Oracle ASM volumes. The value must be set to 11.2 or higher. Before setting this attribute, the COMPATIBLE.ASM value must be 11.2 or higher. Also, the Oracle ADVM volume drivers must be loaded in the supported environment.
By default, the value of the COMPATIBLE.ADVM attribute is empty until set.
CONTENT.TYPE
The CONTENT.TYPE attribute identifies the disk group type: data, recovery, or system. The type value determines the distance to the nearest neighbor disk in the failure group where Oracle ASM mirrors copies of the data. The default value is data which specifies a distance of 1 to the nearest neighbor disk. A value of recovery specifies a distance of 3 to the nearest neighbor disk and a value of system specifies a distance of 5.
The attribute can be specified when creating or altering a disk group. If CONTENT.TYPE attribute is set or changed using ALTER DISKGROUP, then the new configuration does not take effect until a disk group rebalance is explicitly run.
The CONTENT.TYPE attribute is only valid for disk groups that are set to normal or high redundancy. The COMPATIBLE.ASM attribute must be set to 11.2.0.3 or higher to enable the CONTENT.TYPE attribute for the disk group.
The attribute can be set with SQL, ASMCMD, or ASMCA. For example:

SQL> CREATE DISKGROUP data NORMAL REDUNDANCY

        FAILGROUP controller1 DISK

        '/devices/diska1' NAME diska1,

...

        ATTRIBUTE 

        'compatible.asm' = '11.2.0.3', 

        'content.type' = 'recovery',

...

SQL> ALTER DISKGROUP data SET ATTRIBUTE 'content.type' = 'data';

This attribute is primarily intended for use with Oracle Exadata storage.
DISK_REPAIR_TIME
This attribute can only be set when altering a disk group.

Oracle ASM Fast Mirror Resync

Restoring the redundancy of an Oracle ASM disk group after a transient disk path failure can be time consuming. This is especially true if the recovery process requires rebuilding an entire Oracle ASM failure group. Oracle ASM fast mirror resync significantly reduces the time to resynchronize a failed disk in such situations. When you replace the failed disk, Oracle ASM can quickly resynchronize the Oracle ASM disk extents.

Note:

To use this feature, the disk group compatibility attributes must be set to 11.1 or higher. For more information, refer to "Disk Group Compatibility".

Any problems that make a failure group temporarily unavailable are considered transient failures that can be recovered by the Oracle ASM fast mirror resync feature. For example, transient failures can be caused by disk path malfunctions, such as cable failures, host bus adapter failures, controller failures, or disk power supply interruptions.
Oracle ASM fast resync keeps track of pending changes to extents on an OFFLINE disk during an outage. The extents are resynced when the disk is brought back online.
By default, Oracle ASM drops a disk in 3.6 hours after it is taken offline. You can set the DISK_REPAIR_TIME disk group attribute to delay the drop operation by specifying a time interval to repair the disk and bring it back online. The time can be specified in units of minutes (m or M) or hours (h or H). If you omit the unit, then the default unit is hours. The DISK_REPAIR_TIME disk group attribute can only be set with the ALTER DISKGROUP SQL statement.
If the attribute is not set explicitly, then the default value (3.6h) applies to disks that have been set to OFFLINE mode without an explicit DROP AFTER clause. Disks taken offline due to I/O errors do not have a DROP AFTER clause.
The default DISK_REPAIR_TIME attribute value is an estimate that should be adequate for most environments. However, ensure that the attribute value is set to the amount of time that you think is necessary in your environment to fix any transient disk error, and that you are willing to tolerate reduced data redundancy.
The elapsed time (since the disk was set to OFFLINE mode) is incremented only when the disk group containing the offline disks is mounted. The REPAIR_TIMER column of V$ASM_DISK shows the amount of time left (in seconds) before an offline disk is dropped. After the specified time has elapsed, Oracle ASM drops the disk. You can override this attribute with the ALTER DISKGROUP OFFLINE DISK statement and the DROP AFTER clause.

Note:

If a disk is offlined by Oracle ASM because of an I/O (write) error or is explicitly offlined using the ALTER DISKGROUP... OFFLINE statement without the DROP AFTER clause, then the value specified for the DISK_REPAIR_TIME attribute for the disk group is used.

Altering the DISK_REPAIR_TIME attribute has no effect on offline disks. The new value is used for any disks that go offline after the attribute is updated. You can confirm this behavior by viewing the Oracle ASM alert log.
If an offline disk is taken offline for a second time, then the elapsed time is reset and restarted. If another time is specified with the DROP AFTER clause for this disk, the first value is overridden and the new value applies. A disk that is in OFFLINE mode cannot be dropped with an ALTER DISKGROUP DROP DISK statement; an error is returned if attempted. If for some reason the disk must be dropped (such as the disk cannot be repaired) before the repair time has expired, a disk can be dropped immediately by issuing a second OFFLINE statement with a DROP AFTER clause specifying 0h or 0m.
You can use ALTER DISKGROUP to set the DISK_REPAIR_TIME attribute to a specified hour or minute value, such as 4.5 hours or 270 minutes. For example:

ALTER DISKGROUP data SET ATTRIBUTE 'disk_repair_time' = '4.5h'

ALTER DISKGROUP data SET ATTRIBUTE 'disk_repair_time' = '270m'

After you repair the disk, run the SQL statement ALTER DISKGROUP ONLINE DISK. This statement brings a repaired disk group back online to enable writes so that no new writes are missed. This statement also starts a procedure to copy of all of the extents that are marked as stale on their redundant copies.
If a disk goes offline when the Oracle ASM instance is in rolling upgrade mode, the disk remains offline until the rolling upgrade has ended and the timer for dropping the disk is stopped until the Oracle ASM cluster is out of rolling upgrade mode. See "Using Oracle ASM Rolling Upgrade". Examples of taking disks offline and bringing them online follow.
The following example takes disk DATA_001 offline and drops it after five minutes.

ALTER DISKGROUP data OFFLINE DISK DATA_001 DROP AFTER 5m;

The next example takes the disk DATA_001 offline and drops it after the time period designated by DISK_REPAIR_TIME elapses:

ALTER DISKGROUP data OFFLINE DISK DATA_001;

This example takes all of the disk in failure group FG2 offline and drops them after the time period designated by DISK_REPAIR_TIME elapses. IF you used a DROP AFTER clause, then the disks would be dropped after the specified time:

ALTER DISKGROUP data OFFLINE DISK IN FAILGROUP FG2;

The next example brings all of the disks in failure group FG2 online:

ALTER DISKGROUP data ONLINE DISK IN FAILGROUP FG2;

This example brings only disk DATA_001 online:

ALTER DISKGROUP data ONLINE DISK DATA_001;

This example brings all of the disks in disk group DATA online:

ALTER DISKGROUP data ONLINE ALL;

Querying the V$ASM_OPERATION view while you run any of these types of ALTER DISKGROUP ... ONLINE statements displays the name and state of the current operation that you are performing. For example, the query:

SELECT GROUP_NUMBER, OPERATION, STATE FROM V$ASM_OPERATION;

Displays output similar to the following:

GROUP_NUMBER OPERA STAT 

------------ ----- ---- 

           1 ONLIN RUN 

An OFFLINE operation is not displayed in a V$ASM_OPERATION view query.
IDP.BOUNDARY and IDP.TYPE
These attributes are intended for use with Oracle Exadata storage.
SECTOR_SIZE
This attribute can only be set when creating a disk group.

Specifying the Sector Size for Drives

You can use the optional SECTOR_SIZE disk group attribute with the CREATE DISKGROUP SQL statement to specify disks with the sector size set to the value of SECTOR_SIZE for the disk group. Oracle ASM provides support for 4 KB sector disk drives without negatively affecting performance. The SECTOR_SIZE disk group attribute can be set only during disk group creation.
The values for SECTOR_SIZE can be set to 512, 4096, or 4K if the disks support those values. The default value is platform dependent. The COMPATIBLE.ASM and COMPATIBLE.RDBMS disk group attributes must be set to 11.2 or higher to set the sector size to a value other than the default value.

Note:

Oracle Automatic Storage Management Cluster File System (Oracle ACFS) does not support 4 KB sector drives. There is a performance penalty for Oracle ACFS when using 4 KB sector disk drives in 512 sector emulation mode.

The following validations apply to the sector size disk group attribute.

·         Oracle ASM prevents disks of different sector sizes from being added to the same disk group. This validation occurs during CREATE DISKGROUP, ALTER DISKGROUP ADD DISK, and ALTER DISKGROUP MOUNT operations.

·         If the SECTOR_SIZE attribute is explicitly specified when creating a disk group, then Oracle ASM attempts to verify that all disks discovered through disk search strings have a sector size equal to the specified value. If one or more disks were found to have a sector size different from the specified value, or if Oracle ASM was not able to verify a disk sector size, then the create operation fails.

Oracle ASM also attempts to verify disk sector size during the mount operation and the operation fails if one or more disks have a sector size different than the value of the SECTOR_SIZE attribute.

·         If the SECTOR_SIZE attribute is not specified when creating a disk group and Oracle ASM can verify that all discovered disks have the same sector value, then that value is assumed for the disk group sector size that is created. If the disks have different sector sizes, the create operation fails.

·         When new disks are added to an existing disk group using the ALTER DISKGROUP .. ADD DISK SQL statement, you must ensure that the new disks to be added have the same value as the SECTOR_SIZE disk group attribute. If the new disks have different sector sizes, the alter operation fails.

·         You can determine the sector size value that has either been assumed or explicitly set for a successful disk group creation by querying the V$ASM_ATTRIBUTE view or run the ASMCMD lsattr command. You can also query the SECTOR_SIZE column in the V$ASM_DISKGROUP view.

·         SQL> SELECT name, value FROM V$ASM_ATTRIBUTE 

·              WHERE name = 'sector_size' AND group_number = 1;

·         NAME                        VALUE

·         --------------------------- -----------------------

·         sector_size                 512

·          

·         SQL> SELECT group_number, sector_size FROM V$ASM_DISKGROUP 

·              WHERE group_number = 1;

·          

·         GROUP_NUMBER SECTOR_SIZE

·         ------------ -----------

·                    1         512

·         Not all disks support all of the possible SECTOR_SIZE values. The sector size attribute setting must be compatible with the physical hardware.

As shown in Example 4-3, you can use the SECTOR_SIZE attribute with the CREATE DISKGROUP SQL statement to specify the sector size of the disk drive on which the Oracle ASM disk group is located.

Example 4-3 Creating a disk group of 4K sector size

CREATE DISKGROUP data NORMAL REDUNDANCY

FAILGROUP controller1 DISK

'/devices/diska1',

'/devices/diska2',

'/devices/diska3',

'/devices/diska4'

FAILGROUP controller2 DISK

'/devices/diskb1',

'/devices/diskb2',

'/devices/diskb3',

'/devices/diskb4'

ATTRIBUTE 'compatible.asm' = '11.2', 'compatible.rdbms' = '11.2',

          'sector_size'='4096';

STORAGE.TYPE
The STORAGE.TYPE disk group attribute specifies the type of the disks in the disk group. The possible values are AXIOM, ZFSSA, and OTHER. If the attribute is set to AXIOM or ZFSSA, then all disks in the disk group must be of that type. If the attribute is set to OTHER, then any types of disks can be in the disk group.
If the STORAGE.TYPE disk group attribute is set to AXIOM or ZFSSA, then functionality for Hybrid Columnar Compression (HCC) can be enabled for Pillar Axiom or ZFS storage.