Alireza Kamrani
12/05/2024DISK_REPAIR_TIME:
This attribute specifies the time interval to repair a disk and bring it back online before initiating the drop operation. This attribute can only be set when altering a disk group and is only applicable to normal and high redundancy disk groups.
FAILGROUP_REPAIR_TIME:
This attribute specifies a default repair time for the failure groups in the disk group. The failure group repair time is used if Oracle ASM determines that an entire failure group has failed. The default value is 24 hours (24h).
If there is a repair time specified for a disk, such as with the DROP AFTER clause of the SQL ALTER DISKGROUP OFFLINE DISK statement, that disk repair time overrides the failure group repair time.
This attribute can only be set when altering a disk group and is only applicable to normal and high redundancy disk groups.
More info:
When an transient disk failures happens the time to take to repair the offline disk from mirror groups will be set by diskgroup_repair_time.
For example, If diskgroup_repair_time is set as 3 hours and with in this period if disk repair is not completed, the ASM will drop the disks.
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.
This is called fast mirror resync.
What if total failgroup is having problem, Because failure group outages are more likely to be transient in nature and because replacing all the disks in a failure group is much more expensive operation than replacing a single disk, it would typically make sense for failure groups to have a larger repair time to ensure that all the disks does not get dropped automatically in the event of a failure group outage.
Hence from 12c onwards we have failgroup_repair_time which defaults to 24 hours (diskgroup_repair_time is 3.6 hours)
Difference between a rebalance and resync?
a) Rebalance operation starts when the disk addition/deletion happens using rebalance power until 11, move/copy the extents as a whole to target disk
b) Resync operations comes into picture when the disk becomes online after an offline and using rebalance power from 1 to 1024(12c) and synchronize those extents only not all the extents.
Resync is something like syncronizing the disks with the data that should reside on them. (can be used on transient failure )
Rebalancing is something like spreading the data evenly across all thedisks in a disk group.
(can be used on a disk replace operation)
For more info see:
https://docs.oracle.com/en/database/oracle/oracle-database/21/ostmg/mirroring-diskgroup-redundancy.html#GUID-56B52297-F4E2-4D36-A573-3200A0C78D31
Regards
Alireza Kamrani.
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