Hardware manual

Group Administration Volume replication
12–11
5% + change rate
For example, if you estimate that at most 20% of the volume changes, a value of 25%
might be appropriate
(5% plus 20%).
If you use a local replication reserve value that is less than 100%, suff
icient space might not be available to
maintain the failback snapshot. Therefore, Dell recommends that you select the option that allows you to
borrow free pool space if there is not enough local replication reserve to maintain the failback snapshot.
About delegated space and replica reserve
Replicas are stored in space that the secondary group delegates to the primary group.
For example, if you want to replicate GroupA volumes and Gro
up B volumes to GroupC, GroupC must delegate
space to GroupA and GroupB. See Figure 12-6.
Figure 12-6: Delegated Space
The secondary group administrator delegates space to the primary group when configuring the group as a
replication partner. The administrator can modify the partner configuration and increase or decrease delegated
space.
When the primary group administrator configures a volume for replica
tion, the administrator assigns a portion of
delegated space to the volume. This space, called replica reserve, limits the number of replicas that you can keep
on the secondary group. You can modify the volume replication configuration and increase or decrease the replica
reserve value.
To determine the correct amount of space that the secondary group must delegate to the primary group, you must
obtain
the replica reserve requirement
for each primary group volume that you are replicating to the secondary