Shared volume groups
When creating shared volume groups, typically you can leave the Major Number field blank and let the system provide a default. However, NFS uses volume group major numbers to help uniquely identify exported file systems. Therefore, all nodes to be included in a resource group containing an NFS-exported file system must have the same major number for the volume group on which the file system resides.
In the event of node failure, NFS clients attached to a PowerHA® SystemMirror® cluster operate the same way as when a standard NFS server fails and reboots. Accesses to the file systems hang and then recover when the file systems become available again. However, if the major numbers are not the same, when another cluster node takes over the file system and re-exports the file system, the client application will not recover. The client application will not recover because the file system exported by the node will appear to be different from the one exported by the failed node.