IJ25687: OFFLINE FSCK REPORTS FALSE POSITIVE DUPLICATEDISKADDR CORRUPTIONS BETWEEN SNAPSHOTS

APAR status

• Closed as program error.

Error description

• When a snapshot gets deleted some of the blocks of the
  snapshot are copied to the previous snapshot to maintain
  data and metadata consistency. Now if due to some reason
  when the deletion of the snapshot is interrupted we can have
  a scenario where the blocks are
  copied to the previous snapshot
  but the block disk addresses are not
  yet removed from the snapshot
  being deleted, the status of such
  snapshots change to DeleteRequired.
  This condition is expected for
  DeletedRequired snapshots and will be
  handled properly when the deletion of the snapshot is retried.
  But if before deleting the DeleteRequired
  snapshot if an offline fsck is
  run on the file system then fsck will
  falsely report such blocks as
  duplicate address between the
  DeleteRequired snapshot and its
  previous snapshots.
  

Local fix

• Complete deletion of all the DeleteRequired status
  snapshots before running offline fsck
  

Problem summary

• When a snapshot gets deleted some of the blocks of the
  snapshot are copied to the previous snapshot to maintain
  data and metadata consistency. Now if due to some reason
  when the deletion of the snapshot is interrupted we can have
  a scenario where the blocks are
  copied to the previous snapshot
  but the block disk addresses are not
  yet removed from the snapshot
  being deleted, the status of such
  snapshots change to DeleteRequired.
  This condition is expected for
  DeletedRequired snapshots and will be
  handled properly when the deletion of the snapshot is retried.
  But if before deleting the DeleteRequired
  snapshot if an offline fsck is
  run on the file system then fsck will
  falsely report such blocks as
  duplicate address between the
  DeleteRequired snapshot and its
  previous snapshots.
  

Problem conclusion

• Benefits of the solution:
  With this solution offline fsck will not report false positive
  duplicate address blocks in the snaphots
  Work around:
  Complete deletion of all the DeleteRequired status
  snapshots before running offline fsck
  Problem trigger:
  This issue can occur when the delete of a snapshot has been
  interrupted due to some reason causing the snapshot to now
  show status of DeleteRequired and then offline fsck is run on
  the file system before deleting the DeleteRequired snapshot.
  Symptom:
  Incorrect report of corruptions by fsck
  Platforms affected:
  ALL Operating System environments
  Functional Area affected:
  FSCK
  Customer Impact:
  High Importance
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  IJ27813

Fix information

• Fixed component name

  SPEC SCALE STD

• Fixed component ID

  5737F33AP

Applicable component levels