Hardware manual

Group Administration Volume replication
12–2
How replication works
Before you can replicate volume data, you must configure the group where the volume resides and the group that
stores the volume replicas as replication partners.
Each partner plays a role in the replicatio
n of a volume, and you can monitor replication activity from either
partner:
• Primary group. Location
of the volume. The primary group administrator configures the secondary group as a
replication partner and initiates the volume replication operation. Replication of the volume is considered
outbound from the view of the primary group.
• Secondary group.
Location of the volume’s replica set. The secondary group administrator configures the
primary group as a replication partner and delegates space for storing replicas from the primary group.
Replication of a volume is considered inbound from the view of the secondary group (sometimes called the
destination group).
Mutual authentication using passwords provides
security betwee
n partners.
When you configure the two groups as replication partners, you ca
n configure a volume or volume collection for
replication, specifying the replication partner, the local group space for the replication operation, and the remote
partner space for storing the replicas.
The first time you replicate a volume, the primary group copies the entire contents of
the volume to the secondary
group. For subsequent replication operations, the primary group copies only the data that changed since the
previous replication operation started.
Eventually, the oldest replicas are deleted from the replica se
t to free space for new replicas. The amount of space
you allocate for storing replicas limits the number of replicas you can keep on the secondary group.
Note: To ensure that a complete copy of volume data exists on the
secondary group, the most-recent complete
replica of a volume cannot be deleted.
To access or recover volume data from replicas, you can:
• Clone an individual replica to create a new v
o
lume on the secondary group.
• Promote the replica set to a recovery volume (and snapshots)
on the secondary group and configure initiators to
connect to the recovery volume.
If the primary group becomes available, you can replicate the recovery vo
lume to the primary group and then
fail back to the primary group, returning to the original configuration.
Note: Replication is used primarily
for disaster recovery and does not take the place of a comprehensive backup
strategy.
You can manually delete replicas and replica
sets that are no longer needed. You cannot delete the most recent
complete replica from a replica set, but you can delete the entire replica set, which disables replication on the
volume.