MSA 2040 SMU Reference Guide

128 Using Remote Snap to replicate volumes

3. Map the new primary volume to hosts, as was the original primary volume.

Figure 6 Example of primary-volume failure

If the original primary volume becomes accessible, you can set it to be the primary volume again as described in the

following process overview:

1. Take a snapshot of the original primary volume. This preserves the volume’s current data state for later

comparison with the new primary volume.

2. Remove the volume’s mappings.

3. Set the original primary volume to be a secondary volume.

4. Replicate any data written to the new primary volume to the original primary volume (now a secondary volume).

This can be done as one or more replications. On the final replication, halt host access to the primary volume to

ensure that all data has been transferred to the secondary volume.

5. Set the secondary volume (the original primary volume) to be the new primary volume.

6. You can now mount/present/map the snapshot taken in step 1 and compare it with the new primary volume to

identify any data discrepancies and try to recover any data from the snapshot that would otherwise be lost. For

example, you could use host file-system tools to find any files modified since a certain time, or for a database you

could export any differing records from the snapshot and re-enter them into the current database.

For details, see the procedure to change the primary volume back to the original primary volume in "Changing the

primary volume for a replication set" (page 137).

Remote replication licensing

The Remote Snap feature and the maximum number of snapshots that can be created are separately licensed. By

default, 64 snapshots can be created. Normally, replication snapshots are not accessible to hosts. However, a

replication snapshot can be exported for use as a standard snapshot and will count toward the snapshot license limit.