HP 3PAR Operating System Software - Manual (Page 272)

Snapshots Taken before or during Disaster Recovery
If the Backup System Fails
If the backup system fails, or all communication links to the backup system fail, the primary system:
•
stops the replication of all volume groups
•
takes snapshots of all volumes that were completely synchronized
If the Primary System Fails
When remote copy restarts after a primary system failure (either manually using the
startrcopygroup
command or via the auto_recover policy), HP 3PAR Remote Copy first
looks for a valid resynchronization snapshot for each virtual volume.
•
If a resynchronization snapshot exists, HP 3PAR Remote Copy:
Creates snapshots of all the secondary virtual volumes that were previously synchronized. a.
b.
Resynchronizes the secondary virtual volume by sending only the differences between
the resynchronization snapshot and the current data in the primary virtual volume.
•
If a resynchronization snapshot does not exist, HP 3PAR Remote Copy performs a full
synchronization.
•
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:
a.
Creates a snapshot on that system.
b. Uses this snapshot to resynchronize the natural primary storage system after the primary
system and the links are brought back up and remote copy resumes operations.
For additional information, see the following:
•
“Recovering from Disaster” (page 162)
•
“Error Handling” (page 156)
Snapshots in Asynchronous Periodic Mode
In asynchronous periodic mode, remote copy creates snapshots as part of normal operations.
Snapshots are used to locate the data written between two synchronizations.
Snapshots Taken during Initial Synchronization
During the initial synchronization, HP 3PAR Remote Copy:
1.
Takes a snapshot of the primary volume.
2. Sends that snapshot over to initialize the secondary volume.
Snapshots Taken during Resynchronization
At the next scheduled resynchronization, or whenever you issue the syncrcopy command, HP
3PAR Remote Copy:
1.
Takes new snapshots of the secondary and primary volumes.
2. Sends the differences between the old primary snapshot and the new primary snapshot over
to resynchronize the secondary base volume.
During resynchronization:
•
The secondary volume state is syncing.
•
Just as in synchronous mode, the secondary volume is not in a consistent state because the
updates are written by location order rather than by time order.
272 Remote-Copy Snapshots