Performing the delta resync operation

You perform the delta resync operation using the resynchronize mirrors operation. When the delta resync operation is performed, the differential data will be copied from the TC S-VOL to the UR S-VOL. Review the following important prerequisite information, and then follow the procedure in Resynchronizing a mirror .

• Note the following:
  • The delta resync pair must be created.
  • Remote command devices must be set up.
  • External ports must be set.
  • Mirror IDs must be assigned to remote command devices.

  For details, see Delta resync configuration .

• Required pair and volume statuses:
  • The TC volume used as the 3DC multi-target P-VOL: PAIR
  • The TC S-VOL used as the delta resync P-VOL: SSWS.

    Check this status after executing the CCI horctakeover command

  • The UR delta resync pair: HOLD or HOLDING. If the pair status is HLDE, change to HOLD by performing the pairresync operation.

    This applies to all pairs in the journal in which the UR delta resync pair resides.

  • The UR volume used as the 3DC multi-target and the delta resync pair S-VOL and uses two mirror IDs, one for the 3DC multi-target pair and one for the delta resync pair:

    - 3DC multi-target S-VOL: PAIR, PSUS, or PSUE

    - Delta resync S-VOL: HOLD.

    NoteThe UR S-VOL uses two mirror IDs because of its dual use in the 3DC multi-target and delta resync configurations. The statuses shown above are required for the two mirrors as well as for the journal in which the UR delta resync pair resides.
• If the delta resync S-VOL has been backed up on the secondary site using SI or TI, make sure to review the information for the Delta Resync Failure step in (Changing options used by mirrors ).
• Differential data is stored in the master journal but may not be completely present after a failure at the primary site when the pair was being resynchronized (or after creating the delta resync pair configuration).
• When a UR pair has not been suspended and not resynchronized for a long time, the data in the restore journal might exceed 70% of capacity and old journal data is automatically deleted. In this case, the P-VOL and S-VOL are not synchronized completely by just copying the data, and delta resync will fail. In case of delta resync failure, based on Delta Resync Failure settings, the entire P-VOL data will be copied to the S-VOL or pair status becomes HLDE with no processing and delta resync ends abnormally.
• Journal data may also be destroyed in the following cases:
  • When you restore the TC or UR pair in the multi-target configuration, and then also update the delta resync pair.
  • When retry-processing occurs because of a delay of the P-VOL update.
  • When the update of a TC S-VOL is delayed.
• The UR pair status in a delta resync configuration could become PSUS or PSUE if you split the pair, or if there is a failure when copying all data from the P-VOL to the S-VOL. If you then run the delta resync operation, all data might be copied from P-VOL to S-VOL regardless of journal option settings.
• If the pair’s mirror is in Halting or Stopping status, the resynchronization command is rejected.