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: