Interesting issue has cropped up. I think it happened after a power failure.... One of my USB external Samsung 2TB drives (in a 2 bay Rosewill USB case) can no longer be seen from the MAC (a Intel Mini running 10.8.2) it's connected to. However....other MACs on my internal network can see the drive, and it appears to be operating normally (other than not being seen on the MAC it's connected to). Other MACs (various OSes) can see the drive, write to it, read from it, copy files to it, delete files on it, etc. etc. On the MAC it's connected to....Disk Utility can see the drive. It can verify the drive ('the volume xxxx appears to be OK'). However, it can't repair the drive...DU says it 'can't unmount the drive'. And...the 'verify disk permissions' and 'repair disk permissions' options are 'greyed' out. Any ideas on what to do? It is backed up....but would love to have it completely operational (of course). Thanks in advance!