Methods to repair metadata and data block replica mismatches

Use this information to learn about the methods that can be used to repair metadata and data block replica mismatches.

You can repair metadata block replica mismatches with the -m option of offline fsck. Using an offline fsck is a requirement because metadata blocks can have two valid but inconsistent replicas. If the chosen reference replica block happens to be the stale one, it can cause inconsistencies for other dependent metadata. Such resulting inconsistencies can be repaired reliably by offline fsck only. For more information, see mmfsck command.

Metadata block replica mismatches must be repaired before you can attempt to repair data block replica mismatches. Otherwise, IBM Storage Scale might read data blocks from the bad metadata block replicas and cause file system corruption during repair.

After any metadata block replica mismatches are repaired, the file system can be brought online. Then, you can run an online replica compare operation to find the data block replica mismatches with the following command:

mmrestripefs <fs> --check-conflicting-replicas

This command will report replica mismatches with output similar to the following:

…
Scanning user file metadata …
Inode 9824 [fileset 0, snapshot 0 ] has mismatch in replicated disk address 1:173184 3:135808 at block 207
Inode 10304 [fileset 0, snapshot 0 ] has mismatch in replicated disk address 2:145792 1:145920 at block 1
…

You can choose from two methods to resolve the data block replica mismatches. Both options require the data block replica repair feature to be enabled with the following command:

mmchconfig readReplicaRuleEnabled=yes -i

This configuration option can be enabled and disabled dynamically, so you do not need to restart the GPFS daemon. You might experience a small impact on performance for file reads due to enabling the configuration option. It is advised to turn off this configuration option after all of the data block replica mismatches are repaired. Also, it is advised to turn off this configuration option while performing operations like restriping and rebalancing the file system. For more information about the two methods to resolve the data block replica mismatches, see Repairing data block replica mismatches with the global replica selection rule and Repairing data block replica mismatches with the file level replica selection rule.