Sometimes when an ESS vpath disk has previously been assigned to AIX and is now assigned to Windows, or vice versa, you aren’t able to access the disk even when it all looks correct. The first thing to check is whether the vpath still has a persistant reservation on it.

In AIX this is easy, run ‘lquerypr -vh /dev/vpathXX’ to see if a vpath has a persistant reservation, then ‘lquerypr -ch /dev/vpathXX’ to clear the reservation