I have a HD that intermittently mounts/dismounts without any input from me. My setup is as follows: HD #1 is the problem HD; it is connected to iMac via Thunderbolt/firewire adapter. HD #2 is daisy chained to #1 via firewire 800/400 cable. Equipment is late 2013 iMac with Maverick OS. As stated above HD #1 will mount on the desktop and then without any input from me it will suddenly dismount. Later it will suddenly mount again. This activity continues to repeat over and over. I have no problems with HD #2. Thanks for your help.