Hardware manual

Group Administration Volume replication
12–12
group. Replica reserve is based on a percentage of the volume’s replica volume reserve. See Replica volume
reserve and Replica reserve usage.
Replica volume reserve
Each replicated volume has a replica volume reserve, which approximates the amount of in-use volume space. The
value of the replica volume reserve is used to allocate replica reserve for a volume.
When you configure a volume for replication, the primary group sets
the initial value of the replica volume reserve:
• For volumes that are not thin-provisioned
, 10% of the reported volume size.
For example, if you have a 10 GB volume that is not thin-provisioned, the
initial replica volume reserve is 1
GB (10% of 10 GB).
• For thin-provisioned volumes, the current volume reserve.
For exa
mple, if you have a 10 GB volume that is
thin-provisioned with a volume reserve of 2.5 GB, the initial
replica volume reserve is 2.5 GB.
The initial value of the replica volume reserve appears
in the Configure Replication – General Settings dialog box.
At the start of each replication operation, the primary group dete
rmines whether to increase the value of the replica
volume reserve:
• For volumes that are not thin-provisioned
, the replica volume reserve increases by the amount of new data
added to the volume since the start of the previous successful replication, up to the reported volume size. That
is, the replica volume reserve increases by the amount of data that must be replicated.
For example, if you have a 10 GB volume that is not thin-provisioned,
and initiators write 2 GB to the volume,
the replica volume reserve increases by 2 GB.
• For thin-provisioned volumes, the replica volume rese
rve increases to the current size of the volume reserve,
up to the maximum in-use space value.
For example, if you have a 10 GB volume that is thin
-provisioned, and the volume reserve increases from 2.5
GB to 4.0 GB, the replica volume reserve increases by 1.5 GB.
The size of the replica reserve for a volume is based on a percen
tage of the replica volume reserve. Therefore, as
the replica volume reserve increases, the replica reserve also increases, providing more space for replicas, up to a
limit. See Replica reserve usage.
Replica reserve usage
To provide space for partner replicas, the secondary group delegates space to the partner. When you configure a
volume for replication, you assign a portion of delegated space to the volume. This space, called replica reserve,
limits the number and size of volume replicas that you can keep on the secondary group.
It is important to correctly size the replica reserve for a volume. To
o little replica reserve might prevent you from
keeping the desired number of replicas. However, delegated space is limited, so keeping too many replicas might
not be an efficient use of delegated space.