Hardware manual

Group Administration Volume replication
12–8
See About delegated space and replica reserve on page 1
2-11 and Replica reserve usage on page 12-12.
To make sure replication operations complete and to keep the desi
red number of volume replicas, you must allocate
sufficient replication space.
To determine the optimal amount of replication space, Dell recommends
that you set up replication using the
default space values, monitor activity over some time period, analyze the space usage, and make adjustments. This
helps you keep the desired number of replicas while using replication space efficiently.
About local replication reserve
Each replicated volume requires primary group space, called local replication reserve. See Figure 12-5.
Figure 12-5: Local Replication Reserve
Local replication reserve has two purposes:
• Preserve the contents of the volume at the time replication started. If volume
writes occur during a
replication operation, the primary group creates a snapshot of the volume in the local replication reserve to
preserve the contents of the volume at the time replication started. As volume changes occur during replication,
the snapshot consumes more local replication reserve.
When replication completes, the prima
ry group de
letes the snapshot, freeing the space, unless you chose the
option to keep the failback snapshot.
• Store the failback snapshot (optional). The fa
ilback snapshot for a volume can expedite volume failback
operations.
If you choose to keep the failback snapshot when config
uring a volume for replication, the primary group does
not delete the snapshot in the local replication reserve when replication completes. Instead, it becomes the
failback snapshot. As volume changes occur between replication operations, the failback snapshot consumes
more local replication reserve.