HP 3PAR Operating System Software - Manual (Page 273)

•
When the resynchronization completes, remote copy deletes the old snapshots on the primary
and the backup systems.
•
After resynchronization, the base volume on the backup storage system matches the new
snapshot on the primary storage system. The new snapshot on the primary system can now
be used in the next resynchronization operation.
Snapshots and Resynchronization Failure in Asynchronous Periodic Mode
If, during resynchronization in asynchronous periodic mode, the primary system fails or all of the
remote-copy links fail, remote copy behaves in the following manner for the volumes in the
remote-copy target volume group:
•
For all volumes in the remote-copy volume group that completed resynchronizing before the
failure, HP 3PAR Remote Copy takes no action on these volumes and retains all
pre-synchronization snapshots for these volumes.
•
For all volumes in the remote-copy volume group that were in the process of resynchronizing
at the time of the failure, but that did not complete resynchronizing, HP 3PAR Remote Copy
automatically promotes the pre-synchronization snapshot for all of these volumes.
NOTE: The duration of this promotion operation is proportional to the amount of data
changed before the resynchronization failed.
•
For all volumes in the remote-copy volume group that had not started resynchronization at the
time of failure, HP 3PAR Remote Copy does nothing.
This means that if, at the time of the failure, some of the volumes in the volume group successfully
synchronized before the failure, and some volumes did not finish resynchronizing before the failure,
then the volumes that had not completed resynchronization will be promoted to the last recovery
point and volumes that had completed their resynchronization will be left unchanged at the current
recovery point. At this point in time. the volumes on the target array are not in an I/O consistent
state. Any snapshots taken from these targets will not be usable. To make the volumes I/O consistent
again, one of two actions must be performed:
•
The remote-copy volume group must be restarted after the failure has been recovered from,
at which time a new resynchronization will occur, resulting in all the volumes becoming I/O
consistent with one another at the new resynchronization point in time.
•
The remote-copy volume group must be used for recovery, by means of a failover, at which
time all of the volumes whose snapshots were not promoted following the failure (the ones
that completed synchronization) will have their pre-synchronization snapshots promoted, and
all the volumes in the volume group will then revert to their I/O consistent pre-synchronization
state.
Snapshots Taken before or during Disaster Recovery
If the backup storage system is temporarily converted to a primary storage system (for example,
during disaster recovery or as part of planned downtime), HP 3PAR Remote Copy:
1.
Creates a snapshot on the natural backup system.
2. Uses this snapshot to resynchronize the natural primary system after the primary system and
the links are brought back up and remote copy resumes operations.
For additional information, see “Recovering from Disaster” (page 162)
Snapshots in Asynchronous Periodic Mode 273