Why is the disk group I want not available?

When you add capacity to a , the disk group might not appear in the display list for these reasons:

There are no available physical disks of the same physical disk type as the physical disks that comprise the disk group.
There are no unassigned physical disks in the .
One or more in the disk group are in a Failed, Offline, or Degraded state.
One or more virtual disks in that disk group are a source or target for a virtual disk copy. The copy status is currently Pending or In Progress.