Asynchronous mirroring - Why don’t I see all my volumes?
When you are selecting a primary volume for a mirrored pair, a list shows all the eligible volumes.
Any volumes that are not eligible to be used do not display in that list. Volumes may not be eligible for any of the following reasons:
The volume is not optimal.
The volume is already participating in a mirroring relationship.
For thin volumes, auto-expansion must be enabled.