Dell PowerVault ME4 Series Storage System Administrator’s Guide

Initial replication

The following illustration shows the internal processes that take place during the initial replication of a single volume.

The two internal snapshots for each volume on the primary and secondary systems all have distinct roles. For both systems, they are labeled S1 (Snapshot 1) and S2 (Snapshot 2) in the two figures above and below. When a replication set is created, the primary volume and its internal snapshots all contain the same data. The secondary volume and its internal snapshots do not contain any data. Between the time that the replication set was created and the initial replication occurs, it is possible that hosts have written additional data to the primary volume.

During initial replication, the following sequence takes place. The user initiates replication on the primary system (step 1). The current primary volume contents, which might be different than when the replication set was created, replace the contents of S1 on the primary system (step 2). The S1 data, which matches that of the primary volume, is replicated in its entirety to its S1 counterpart on the secondary system and replaces the data that the secondary system S1 contains (step 3). The S1 contents on the secondary system replace the contents of the secondary volume (step 4). The contents of the primary and secondary volumes are now synchronized.