Dell PowerVault ME4 Series Storage System Administrator’s Guide

Replication prerequisites

To replicate a volume, you must first create a peer connection and replication set. A peer connection establishes bi-directional communication between a local and remote system, both of which must have FC or iSCSI ports and a virtual pool. The system establishes a peer connection by connecting a host port on the local system with a user-specified host port on the remote system, then exchanging information and setting up a long term communication path in-band. Because the communication path establishes a peer connection between the two systems, replications can occur in either direction.

To verify that a host port address is available before creating a peer connection, use the query peer-connection CLI command. This command provides information about the remote system, such as inter-connectivity between the two systems, licensing, and pool configuration. For more information on this command, see the Dell PowerVault ME4 Series Storage System CLI Guide. For more information on peer connections, see Creating a peer connection, Deleting a peer connection, and Modifying a peer connection.

Internal snapshots and internal volume groups count against system limits, but do not display.

Using a volume group for a replication set enables you to make sure that 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. Even though the snapshots may differ in size, replication is not complete until all of the snapshots are replicated.

For a replication set, the term primary refers to the source volume and the system in which it resides, and the term secondary is used for the remote copy and the system in which it resides. The secondary volume is meant to be an exact copy of the primary volume from the last time that replication occurred. To guarantee that the contents from that point in time match, the secondary volume cannot be mapped, rolled back, or modified except through replication.

While you cannot modify the secondary volume, you can create a snapshot of the secondary volume that you can map, roll back, and otherwise treat like any volume or snapshot. You can regularly take snapshots to maintain a history of the replications for backup or archiving, or enable snapshot history for the replication set. These snapshots also can be used in disaster recovery. For more information on replication sets, see “Creating a replication set from the Replications topic, Creating a replication set from the Volumes topic, Modifying a replication set, and Deleting a replication set.