After installing Mavericks on my Mac Pro (mid 2012) the internal drives (3) randomly un-mount. I have a mix of 2 SSD (180G Operating System drive and a 500G) and 2 HDD ( 1TB and 2TB). both type of drives have un-mounted on me, with the exception of the OS drive.
Mac Pro (Mid 2012), OS X Mavericks (10.9)
I have a very similar issue with Mac Pro (4,1, early 2009). None of my internal HDDs disconnect, but the SSD installed in the optical bay (OWC Mercury Electra 3G with upgraded firmware, 240GB drive) disconnects often - especially after sleep/wake from the looks of it. Since it was the OS drive, I have removed it for now pending a solution.
One thing that may be worth a shot is formatting those drives because SSD's have the same tech as flash drives. After a certain amount of uses, the drive dies. other thing you could do is go into disk utility and repair the disk or its permissions. something similar happened to me before andthis seemed to do the trick. glhf and hope this helps🙂
Mavericks
