Handling Mount Points in Promoted Mirror Volumes

Explains how to use mount points in promoted mirror volumes.

After you promote read-only mirror volumes to read-write standard volumes, you must re-establish the mount points that were set up in the source cluster. To understand the steps in this process, consider the following scenario:

A source cluster has volumes A, B, and C, which are mounted at /A, /A/B, and /A/B/C respectively. Each source volume is mirrored to a volume in another cluster (the destination cluster). The names of the corresponding mirror volumes are also A, B, and C.

NOTE
When you use promotable mirrors, the volumes on the destination cluster must be set up in the same way as on the primary site. This means that volume names are the same and mount points are the same. If a hierarchical mounting structure (such as /A/B) is used on the primary site, the same structure must be recreated once mirror volumes are promoted at the secondary site.

Mirror volume A is mounted at /A, but since the mirror is read-only, no mount point can be created beneath it for mirror B or mirror C.



WARNING
Mirror volumes that are promoted to standard (read-write) volumes are not available for write operations until they are mounted explicitly.

Now suppose that all three mirror volumes are promoted to read-write volumes. Before any data can be written to these volumes, the volume links must be removed and the volumes must be remounted. The commands for each step are as follows:

  1. Promote A, B, and C to read-write volumes.
    Cluster2> maprcli volume modify -name A -type rw
Cluster2> maprcli volume modify -name B -type rw
Cluster2> maprcli volume modify -name C -type rw

    To promote using the Control System, see Changing Mirror Volumes to Standard Volumes.

  2. Remove the volume links located at /A/B and /A/B/C. Since mirror A was already mounted, its volume links do not need to be removed. 
    maprcli volume link remove -path /A/B 
maprcli volume link remove -path /A/B/C
  3. Mount the promoted read-write volumes B and C at the same mount points used in the primary (source) cluster, in order to maintain an exact replica in the destination cluster.
    Cluster2> maprcli volume mount -name B -path /A/B 
Cluster2> maprcli volume mount -name C -path /A/B/C

    To mount using the Control System, see Mounting one or more Volumes.

Now the promoted volumes are accessible for write operations.