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Retrieving data for disaster recovery: A special use of snapmirror resync

When disaster disables the source of a SnapMirror relationship, you can use the snapmirror resync command as part of a strategy to update the repaired source and reestablish the original configuration of the systems.

About this task

In the following example, the original source (the one disabled by the disaster) is systemA:vol/volA and the original destination is systemB:/vol/volB. You use a combination of snapmirror break and snapmirror resync or snapmirror initialize commands to perform the following tasks:

In this example, all data from the last scheduled SnapMirror Snapshot copy before the source was disabled and all the data written to systemB:vol/volB after it was made writable is preserved. Any data written to systemA:vol/volA between the last SnapMirror Snapshot copy and the time that systemA:vol/volA was disabled is not preserved.


  1. After the source volume (in this case, systemA:volA) is disabled, use the snapmirror break command to make the destination volume, systemB:volB, writable.
    snapmirror break systemB:volB
  2. Redirect the clients of source systemA to source systemB.

    The former clients of systemA are now accessing and writing to systemB.

  3. Temporarily make the original source volume a read-only destination volume.

    • If systemA:volA is recoverable, and its data is intact, then use the snapmirror resync command on systemA to resynchronize systemA with systemB.
      snapmirror resync -S systemB:VolB systemA:volA
    • If systemA:volA is unrecoverable, make a new volA on systemA, and from systemA, initialize systemA:volA from systemB.
      snapmirror initialize -S systemB:volB systemA:volA

      This command also makes systemA:volA a read-only destination.

    Note: These commands need to be performed on the original source system.

  4. Redirect the clients from systemB to systemA.

    The clients cannot access or write to systemA:volA, but they are no longer writing new data to systemB:volB.

  5. Update systemA:volA from systemB to transfer the latest data from systemB.


    Perform the following step from systemA:

    snapmirror update -S systemB:volB systemA:volA

  6. Use the snapmirror break command to make systemA:volA writable. On systemA, enter the following command:
    snapmirror break volA
  7. On systemB, use the snapmirror resync command to make systemB, the original destination, the destination again.
    snapmirror resync volB