Fast mirror resynchronization in ASM 11g

Fast Mirror resync in ASM 11g new feature

In Oracle 10g, If a disk of an disk group is unavailable for only a short period of time due to cable disconnect or any other reason, then server remove the disk from diskgroup instead of waits for the disk to become available again. ASM start the re-balance operation for the disk group. After reading the disk then it need to re-balance again. So to avoid this extra I/O operation in 11g introduced the FAST Mirror Re-synchronization in ASM.

In 11g Fast mirror resync, If disk is available with in the time limit of parameter DISK_REPAIR_TIME then rebalance operation is only done for modified blocks after the disk temporary unavailable and available with in the time limit of parameter.

Default of disk_repair_time is 3.6 hours.

For use this feature both having in 11g:

ALTER DISKGROUP SET ATTRIBUTE 'compatible.asm'='11.1';

ALTER Diskgroup SET ATTRIBUTE 'compatible.rdbms' = '11.1';

Disk group attribute disk_repair_time to determine how long to wait before an ASM disk is permanently dropped from an ASM disk group after it was taken offline for whatever reason. The default of disk_repair_time is 3.6 hours(190 Minutes)

For Disable this 11g feature:
Set DISK_REPAIR_TIME parameter to the value 0.

Change the parameter from default 3.6 to 24 hours:

alter diskgroup set attribute 'DISK_REPAIR_TIME'='24H';

 
Drop disk before repair time expired

Alter diskgroup offline disk disk1_001 drop after 0m;

Check the ststus of ASM diskgroup disks and Repair time value:

-- Online the disk
ALTER DISKGROUP DISK ONLINE;

select * from v$asm_disk_stat;

-- check compatibility
select * from v$asm_attribute;

--show the current disk repair time attribute value
select * from V$asm_disk;

Note: v$asm_disk has a column REPAIR_TIMER which shows the number of seconds remaining until the disk is automatically dropped and 0 if not failed.

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