Disks Operations in ASM

Rebalance Disk Group

·         ASM rebalance a disk group automatically, whenever we add or remove disks form disk group.

·         Disk groups can be rebalanced manually using the REBALANCE clause of the ALTER DISKGROUP statement.

·         If the POWERclause is omitted the ASM_POWER_LIMIT parameter value is used.

Example :

SQL> ALTER DISKGROUP DATA_DG REBALANCE POWER 5;

Mount and Dismount The ASM DISKGROUP

Disk groups are mounted at ASM instance startup and unmounted at ASM instance shutdown. Manual mounting and dismounting can be accomplished using the ALTER DISKGROUP statement as seen below.

ALTER DISKGROUP ALL DISMOUNT;

ALTER DISKGROUP ALL MOUNT;

ALTER DISKGROUP disk_group_1 DISMOUNT;

ALTER DISKGROUP disk_group_1 MOUNT

How to Create DISK GROUP             

SQL> create diskgroup DATA_DG normal redundancy

Failgroup groupA disk ‘/devices/Disk1’, ‘/devices/Disk2’, ‘/devices/Disk3’,

Failgroup groupB disk ‘/devices/DiskD1’, ‘/devices/DiskD2’, ‘/devices/DiskD3’,

When oracle writes data to the disks in the first failure group Group 1, it also wites those extents to disk in the other failure group Group ‘D1’.

Important:

·                     When you don’t specify a FAILGROUP clause, the disk is in its own failure group.

Adding Disks to a Disk Group

ALTER DISKGROUP DATA_DG ADD DISK '/devices/DiskA1’,’/device/DiskB1';

Note:

· When a disk is added, it is formatted and then rebalanced.

·                     When you don’t specify a FAILGROUP clause, the disk is in its own failure group.

·                     When you don’t specify a REDUNDANCY clause, the disk is in its own failure group.

· If you don't specify the NAME clause, Oracle assigns its own system-generated names.

· If the disk already belongs to a disk group, the statement will fail.

Resize a  Disk

· Resize a specific disk.

ALTER DISKGROUP DATA_DG RESIZE DISK DISK1 SIZE 100G;

· Resize all disks in a disk group.

ALTER DISKGROUP DATA_DG RESIZE ALL SIZE 100G;

· Undrop Disk

The UNDROP DISKS clause of the ALTER DISKGROUP statement allows pending disk drops to be undone. It will not revert drops that have completed, or disk drops associated with the dropping of a disk group.

Example :  SQL> ALTER DISKGROUP disk_group_1 UNDROP DISKS;

Dropping Disks and Disk Groups

ALTER DISKGROUP DATA_DG DROP DISK DiskA1;

DROP DISKGROUP DATA_DG INCLUDING CONTENTS;

Note:

· DROP DISKGROUP statements requires the instance to be in MOUNT state.

· When a disk is dropped, the disk group is rebalanced by moving all of the file extents from the dropped disk to other disks in the disk group. The header on the dropped disk is then cleared.

· If you specify the FORCE clause for the drop operation, the disk is dropped even if Automatic Storage Management cannot read or write to the disk.

· You can also drop all of the disks in specified failure groups using the DROP DISKS IN FAILGROUP clause.

DISK STATUS in ASM

·                     UNPROTECTED - No mirroring or striping regardless of the redundancy setting.

·                      MIRROR - Two-way mirroring for normal redundancy and three-way mirroring for high redundancy. This attribute cannot be set for external redundancy.

·                     COARSE - Specifies lower granuality for striping. This attribute cannot be set for external redundancy.

·                     FINE - Specifies higher granularity for striping. This attribute cannot be set for external redundancy.

See Also                                                                                               See Also 

Rename Disk / Delete Disk in ASM                                                        Moving Control Files in ASM