To group volumes or disks differently as the needs of your organization change. For example, you might want to split disk groups to match the boundaries of separate departments, or to join disk groups when departments are merged.
To isolate volumes or disks from a disk group, and process them independently on the same host or on a different host. This allows you to implement off-host processing solutions for the purposes of backup or decision support.
To reduce the size of a disk group's configuration database in the event that its private region is nearly full. This is a much simpler solution than the alternative of trying to grow the private region.
The vxdg command provides the following operations for reorganizing disk groups:
The move operation moves a self-contained set of VxVM objects between imported disk groups. This operation fails if it would remove all the disks from the source disk group. Volume states are preserved across the move.
Figure: Disk group move operation shows the move operation.
The split operation removes a self-contained set of VxVM objects from an imported disk group, and moves them to a newly created target disk group. This operation fails if it would remove all the disks from the source disk group, or if an imported disk group exists with the same name as the target disk group. An existing deported disk group is destroyed if it has the same name as the target disk group (as is the case for the vxdg init command).
Figure: Disk group split operation shows the split operation.
Figure: Disk group join operation shows the join operation.
These operations are performed on VxVM objects such as disks or top-level volumes, and include all component objects such as sub-volumes, plexes and subdisks. The objects to be moved must be self-contained, meaning that the disks that are moved must not contain any other objects that are not intended for the move.
For site-consistent disk groups, any of the move operations (move, split, and join) fail if the VxVM objects that are moved would not meet the site consistency conditions after the move. For example, a volume that is being moved may not have a plex on one of the sites configured in the target disk group. The volume would not meet the conditions for the allsites flag in the target disk group. Use the -f (force) option to enable the operation to succeed, by turning off the allsites flag on the object.
If you specify one or more disks to be moved, all VxVM objects on the disks are moved. You can use the -o expand option to ensure that vxdg moves all disks on which the specified objects are configured. Take care when doing this as the result may not always be what you expect. You can use the listmove operation with vxdg to help you establish what is the self-contained set of objects that corresponds to a specified set of objects.
If the system crashes or a hardware subsystem fails, VxVM attempts to complete or reverse an incomplete disk group reconfiguration when the system is restarted or the hardware subsystem is repaired, depending on how far the reconfiguration had progressed. If one of the disk groups is no longer available because it has been imported by another host or because it no longer exists, you must recover the disk group manually.