Administrator Guide

replications. By default, the secondary volume or volume group and infrastructure are created in the pool corresponding to the
one for the primary volume or volume group (A or B). Optionally, you can select the other pool.
A peer connection must be defined to create and use a replication set. A replication set can specify only one peer connection
and pool. When creating a replication set, communication between the peer connection systems must be operational during the
entire process.
If a volume group is part of a replication set, volumes cannot be added to or deleted from the volume group.
If a replication set is deleted, the internal snapshots created by the system for replication are also deleted. After the replication
set is deleted, the primary and secondary volumes can be used like any other base volumes or volume groups.
Primary volumes and volume groups
The volume, volume group, or snapshot that will be replicated is called the primary volume or volume group. It can belong to
only one replication set. If the volume group is already in a replication set, individual volumes may not be included in separate
replication sets. Conversely, if a volume that is a member of a volume group is already in a replication set, its volume group
cannot be included in a separate replication set.
The maximum number of individual volumes and snapshots that can be replicated is 32 in total. If a volume group is being
replicated, the maximum number of volumes that can exist in the group is 16.
Using a volume group for a replication set enables you to make sure that the contents of multiple volumes are synchronized
at the same time. When a volume group is replicated, snapshots of all of the volumes are created simultaneously. In doing so,
it functions as a consistency group, ensuring consistent copies of a group of volumes. The snapshots are then replicated as a
group. Though the snapshots may differ in size, replication of the volume group is not complete until all of the snapshots are
replicated.
Secondary volumes and volume groups
When the replication set is created—either through the CLI or the PowerVault Manager —secondary volumes and volume
groups are created automatically. Secondary volumes and volume groups cannot be mapped, moved, expanded, deleted, or
participate in a rollback operation. Create a snapshot of the secondary volume or volume group and use the snapshot for
mapping and accessing data.
Queuing replications
You can specify the action to take when a replication is running and a new replication is requested.
● Discard. Discard the new replication request.
● Queue Latest. Take a snapshot of the primary volume and queue the new replication request. If the queue contained an older
replication request, discard that older request. A maximum of one replication can be queued. This is the default.
NOTE:
If the queue policy is set to Queue Latest and a replication is running and another is queued, you cannot change
the queue policy to discard. You must manually remove the queued replication before you can change the policy.
Maintaining replication snapshot history from the Volumes topic
A replication set can be configured to maintain a replication snapshot history. As part of handling a replication, the replication
set will automatically take a snapshot of the primary or secondary volumes, or both, thereby creating a history of data that
has been replicated over time. This feature can be enabled for a secondary volume or for a primary volume and its secondary
volume, but not for a volume group.
When this feature is enabled:
● For a primary volume, when a replication starts it will create a snapshot of the data image being replicated.
● For a secondary volume, when a replication successfully completes it will create a snapshot of the data image just
transferred to the secondary volume. (This is in contrast to the primary volume snapshot, which is created before the
sync.) If replication does not complete, a snapshot will not be created.
● You can set the number of snapshots to retain from 1 through 16, referred to as the snapshot retention count. This setting
applies to management of snapshots for both the primary and secondary volume and can be changed at any time. Its value
Working in the Volumes topic
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