Thanks Rottmann,
It was to have an extra copy of critical volumes for a filer move to different location. In our configuration on the HA pair, one head control SAS drives and the other SATA. So there are different physical shelves, so if the SAS shelf is damage on the moving, the volume is on the SATA disks.
We already are doing snap Vault to a 3rd filer so that was enough for us, so I did not have to setup any mirror
Cheers