DFSMShsm and Cascading FlashCopy

With support for Cascading FlashCopy, DFSMShsm lifts some restrictions that previously existed related to FlashCopy and fast replication recovery. See changes marked with revision bars.

Fast replication is a function that uses volume-level fast replication to create backup versions for sets of storage groups. You define a set of storage groups with the SMS copy pool construct. Fast replication target volumes contain the fast replication backup copies of DFSMShsm-managed volumes. Fast replication target volumes are defined with the SMS copy pool backup storage group type. The fast replication backup versions on DASD can then be dumped to tape using either the FRBACKUP command or with Automatic Dump.

Recovery from the fast replication backup versions can be performed at the data set, volume, or copy pool level. The entire copy pool, individual volumes and data sets within a copy pool, can be recovered from the fast replication backup versions on DASD or tape. Individual data sets are recovered to the volume or volumes that they existed on at the time of backup.

The fast replication function enables the backup and recovery of a large set of volumes to occur within a small time frame. The fast replication function supports the FlashCopy® and SnapShot functions.

Impacts to FlashCopy functions supported by DFSMShsm

Cascading FlashCopy impacts support for Incremental FlashCopy, specifically, recovering from a copy pool incremental version, and fast reverse restore, as described below.

Incremental FlashCopy

Incremental FlashCopy provides the capability to refresh a volume in a FlashCopy relationship by copying the changed data only. It reduces background copy time when only a subset of data has changed. An incremental FlashCopy relationship persists until it is withdrawn. DFSMShsm supports incremental FlashCopy in COPY mode.

For more information, see Recovering from a copy pool incremental version.

Fast reverse restore

Fast reverse restore provides the capability to reverse the direction of an existing FlashCopy relationship and restore the source volume to the point-in-time state when it was last flashed to the target without waiting for the background copy to complete. Once a fast reverse restore has completed, the contents of the backup volume (the original FlashCopy target) become invalid. When using fast reverse restore, it is best to keep dump tape copies in addition to DASD copies.

DFSMShsm supports fast reverse restore of a copy pool in both COPY and NOCOPY modes. However, fast reverse restore cannot be used in combination with the preserve mirror operation. When the storage subsystem supports cascaded FlashCopy function, the additional FlashCopy targets will not need to be removed prior to attempting fast reverse restore. Ensure the correct backup version is specified on the command you intend to use for fast reverse restore.

For more information, see Recovering a copy pool using fast reverse restore.