Operating System Software Owner manual

Snapshots in Synchronous Mode
In synchronous mode, Remote Copy creates snapshots only when:
• an error occurs
• disaster recovery is in process
• a volume group is manually stopped
Snapshots and Initial Synchronization Failure
If a failure occurs during the initial (and therefore full) synchronization of a virtual volume:
• Remote Copy does not create a snapshot of that volume.
• After you recover the system and restart Remote Copy, Remote Copy performs another initial
(full) synchronization of the volume.
Snapshots and Resynchronization
During resynchronization:
• The secondary volume state is syncing.
• The secondary volume is not in a consistent state because the updates are written by location
order rather than by time order.
• When the resynchronization completes, Remote Copy deletes the snapshots on the primary
and the backup systems.
NOTE: For more information on deleted snapshots and space re-allocation, see “How CPGs
Allocate Space for Snapshots” (page 187).
Snapshots and Resynchronization Failure
• If the primary system fails during a resynchronization, the secondary base volumes are left in
an inconsistent state, but the snapshots of the secondary volumes are left behind and not
deleted.
• After you recover the primary system, the next resynchronization brings the secondary volumes
back in synchronization with the primary volumes.
• If the primary system fails during a resynchronization and you need to use the backup system
to access data, you must issue failover commands. For more information, see “Recovering
from Disaster” (page 102).
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), Remote Copy first looks for a
valid resynchronization snapshot for each virtual volume.
• If a resynchronization snapshot exists, Remote Copy:
204 Remote Copy Snapshots