Recovering with FlashCopy image copies

Recovering from a FlashCopy® image copy is potentially faster than recovering from a traditional image copy. If an appropriate FlashCopy image copy is available, the RECOVER utility can use it to instantaneously restore an image copy.

About this task

Consider the following information when planning for recovery with FlashCopy image copies:

  • Create both FlashCopy image copies and traditional sequential image copies to provide a complete recovery base for media failures.
  • Creating and recovering from a consistent FlashCopy image copy can consume more processing resources than creating and recovering from a FlashCopy image copy that was not guaranteed to be consistent. To recover from a consistent FlashCopy image copy, the RECOVER utility must read the logs to apply changes that were made to the recovered object after the point of consistency. Some of those changes are likely to be work that was previously backed out and must be reapplied, because the work was uncommitted at the time the FlashCopy image copy was created. (In this case, recovery requires more analysis of the logs during the PRELOGC phase. The preliminary log apply phase, PRELOGA, and the other log phases also require more analysis.) The START_RBA value in the SYSCOPY record of the FlashCopy image copy indicates the low RBA or LRSN of the logs that are needed for processing by RECOVER.
  • Recovering with FlashCopy image copies could prevent a subsequent BACKUP SYSTEM utility job on the same data from completing successfully if the FlashCopy relationship is still outstanding.

    This limitation exists because of the characteristics of FlashCopy relationships. When the RECOVER utility uses fast replication to restore a FlashCopy image copy, it establishes a FlashCopy relationship. This relationship is between the FlashCopy image copy data set (the FlashCopy source) and the underlying data sets for the table space or index space (the FlashCopy target). Cascading FlashCopy relationships, where a data set or extent is both a FlashCopy target and a source, is not supported by the hardware.

    BACKUP SYSTEM also uses FlashCopy technology. Therefore, any of the FlashCopy targets from the RECOVER operation (those underlying data sets for the table space or index space) cannot also be used as a source for BACKUP SYSTEM while the FlashCopy relationship from RECOVER still exists.

    If you plan to use BACKUP SYSTEM, use the REC_FASTREPLICATION subsystem parameter as described in step 1 to control whether the RECOVER utility should use FlashCopy to restore FlashCopy image copies.

  • If the FlashCopy image copy has been migrated or deleted, RECOVER uses the equivalent sequential image copies (created from the FlashCopy image copy) if any exist. Otherwise, the next most recent eligible recovery base is used.

Procedure

To recover with FlashCopy image copies:

  1. Ensure that the REC_FASTREPLICATION subsystem parameter is set to PREFERRED or REQUIRED.

    If this subsystem parameter is set to PREFERRED, RECOVER attempts to use fast replication (FlashCopy) to restore the FlashCopy image copy. Fast replication is not used if the underlying data sets for the table space or index space are already in a FlashCopy relationship due to the BACKUP SYSTEM utility or to the COPY utility. In this case, traditional I/O methods are used instead of fast replication to restore the FlashCopy image copy.

    If this subsystem parameter is set to REQUIRED, RECOVER must use fast replication to restore the FlashCopy image copy. If fast replication cannot be used, the recovery of the object fails. For example, the recovery could fail if the BACKUP SYSTEM utility has established a FlashCopy relationship with the production volume.

    Restriction: If the RECOVER utility establishes a FlashCopy relationship to restore a FlashCopy image copy and the BACKUP SYSTEM utility is started, the creation of the system-level backup might fail. The reason for the failure is because cascading FlashCopy relationships are not supported.

    Otherwise, if this subsystem parameter is set to NONE, RECOVER restores the FlashCopy image copy using traditional I/O methods. Use this option if you use BACKUP SYSTEM and you do not want recovery from FlashCopy image copies to interfere with the creation of system-level backups.

  2. Specify an appropriate RECOVER utility control statement.
    You do not need to specify any extra options in the RECOVER statement to indicate that you want FlashCopy image copies to be used. The RECOVER utility uses FlashCopy image copies if available.

    However, if you specify that RECOVER is to use a specific FlashCopy image copy (by specifying TOCOPY, TOLASTCOPY, or TOLASTFULLCOPY), specify the DSNUM option with the appropriate data set or partition number for the FlashCopy image copy that you want to use.

    If you took FlashCopy image copies at the table space level (by specifying the DSNUM ALL option in the COPY statement), you do not have to recover all of the data sets individually. You can recover the entire table space as one object in the RECOVER statement. Alternatively, you can recover each of the data sets individually.