Administrator Guide

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 must be greater than
the number of existing snapshots in the replication set, regardless of whether snapshot history is enabled. If you select a snapshot
retention count value that is less than the current number of snapshots, an error message is displayed. Thus, you must manually delete
the excess snapshots before reducing the snapshot count setting. When the snapshot count is exceeded, the oldest unmapped
snapshot will be discarded automatically.
• The snapshots are named basename_nnnn where _nnnn starts at 0000 and increments for each subsequent snapshot. If primary
volume snapshots are enabled, snapshots with the same name will exist on the primary and secondary systems. The snapshot number
is incremented each time a replication is requested, whether or not the replication completes — for example, if the replication was
queued and subsequently removed from the queue.
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Working in the Volumes topic