Resynchronizing and restoring ShadowImage pairs

Resynchronizing pairs

You can resynchronize split pairs (PSUS status) and suspended pairs (PSUE status). When you resynchronize a split pair, the differential data on the P-VOL is copied to the S-VOL. When you resynchronize a suspended pair, all data on the P-VOL is copied to the S-VOL. Resynchronizing a suspended pair takes the same amount of time as an initial copy operation.

You can perform the following types of resynchronization operations:

• Normal Copy (full forward resync): Copies differential data from the P-VOL to the S-VOL.

  During a Normal Copy, only the P-VOL is accessible to hosts for read/write operations.

  When the Normal Copy operation is complete, the pair status is changed to PAIR.

• Quick Resync (quick forward resync): Changes the status to RCPY and then changes the pair status to PAIR when the resync operation begins. Copies differential data from the P-VOL to the S-VOL using update copy operations.

  During a Quick Resync, only the P-VOL is accessible to hosts for read/write operations.

By default, for pair resynchronization using Normal Resync, the maximum multiplicity of copy processing for each pair is set to 24 for VSP One Block 20 series and 48 for VSP One Block 85. However, if you set the Normal Resync Multiplexing local replica option to OFF, the multiplicity can be changed to 1. If host I/O performance is prioritized, set the Normal Resync Multiplexing option to OFF.

Restoring pairs

You can restore split pairs (SPLIT status) and suspended pairs (PSUS status). When you restore a split pair, the differential data on the S-VOL is copied to the P-VOL. When you restore a suspended pair, all data on the S-VOL is copied to the P-VOL. Restoring a suspended pair takes the same amount of time as an initial copy operation.

You can perform the following types of restore operations:

• Reverse Copy (full reverse resync): Copies differential data from the S-VOL to the P-VOL.

  During a Reverse Copy, the P-VOL is not accessible to hosts.

  You can delete or suspend pairs during a Reverse Copy operation, but you cannot create, split, or resynchronize pairs that share the same P-VOL.

  If you are sharing a TC or UR volume with a SI volume, you cannot create a TC or UR pair with the shared volume.

• Quick Restore (quick reverse resync):

  For VSP One B85:

  • Swaps the P-VOL and S-VOL including their RAID levels and drive types.
  • Changes the pair status to RCPY and then to PAIR when the quick restore operation begins.
  • Exchanges the P-VOL and S-VOL encryption statuses if the SI pair consists of an encrypted volume and a nonencrypted volume.

  During a Quick Restore, the P-VOL and S-VOL are not accessible. After a Quick Restore, the P-VOL is accessible.

  (VSP One B85) If a pair contains volumes for which Data Retention Utility access attributes are set, Quick Restore does not exchange the P-VOL and S-VOL access attributes.

  (VSP One B85) To keep the P-VOL and the S-VOL from being synchronized after you perform a Quick Restore operation, enable the Swap & Freeze local replica option before you perform Quick Restore. By doing so, the update copy operation is prohibited after Quick Restore is completed and the pair status changes to PAIR.

  (VSP One B85) You can delete or suspend a pair during a Quick Restore operation, but you cannot do the following:

  • Create, split, or resynchronize pairs that share the same P-VOL.
  • Create a TC or UR pair with a volume shared with SI.

  You cannot perform a Quick Restore operation on the following pairs:

  • SI L2 pairs
  • (VSP One B85) Pairs for which you are formatting an internal volume using Quick Format.
  • (VSP One B85) Pairs in which the P-VOL or the S-VOL is a DP-VOL but not both.
  • Pairs in which capacity saving is enabled for the P-VOL or the S-VOL but not both.
  • (VSP One B85) Pairs in which the P-VOL or S-VOL is shared with a TIA volume.

By default, for pair restore using Reverse Copy, the maximum multiplicity of copy processing for each pair is set to 24 for VSP One Block 20 series and 48 for VSP One Block 85. However, if you set the Reverse Copy Multiplexing local replica option to OFF, the multiplicity might be changed to 1. If host I/O performance is prioritized, set the Reverse Copy Multiplexing option to OFF.

If Reverse Copy ends abnormally for VSP One Block 20 series or if Reverse Copy or Quick Restore ends abnormally for VSP One B85, the pair status changes to PSUE. When that occurs, all hosts can write to and read from the P-VOL. However, there is no guarantee that the data in the P-VOL is correct. The S-VOL remains unavailable for writing and there is no guarantee that the data in the S-VOL is correct. The status of other SI pairs sharing the same P-VOL does not change.