Hi All,
I have some stuff to add to this thread.
Most of us here have had some sort of disruption with USB drives, twice I've lost a lot of data, however I've noticed other things that maybe relevant.
The set up with the problem is a mac-mini (2009) 8 gigs of ram on server 10.8.3 when I upgraded to 10.8.1 funny stuff started to happen. I use ARD to connect to the server, I usually don't have the screen on, it stays lights out. But I did have the sleep options switched on in energy saver.
What I found was that after a sleep ARD could no longer connect to the server, although when I switched the screen on everything seemed normal. At that time I didn't much bother playing around and just switched off energy saver. Now at the same time I was getting problems with a USB 2 drive (I have two the same, but only one played up) I thought it more to do with force crashing the machine. I panicked and bought a 3TB USB 3 drive to back up to.
After the 10.8.2 update the USB 2 drive went back to normal, but the USB 3 drive then started to eject. At that time I thought I had drive problems, maybe leads. I had switched energy saver back on as I was running a HD screen most of the time to keep an eye on the server.
In due course I updated to 10.8.3 but still the problems were there. This week my USB 3 drive started fail big time, so I thought the drive must be dead, after it was ejecting I couldn't get it to re-mount disc utilities wouldn't read it, etc.
So I went a bought 2TB USB 3 drive and didn't get a cheap one. When that got ejected I more or less twigged I had a bigger problem and Googled it, I ended up here yesterday. Some of what was being said in this thread confirmed my original suspicions about it being sleep related, but then I found a new twist no one here has mentioned.
So in my case I can corfirm if you turn off all energy saver and screen saver options the drive will stay mounted and behave normally, BUT get this, if you access that disc by AFP on a network and the client computer sleeps while connected that will also unmount it!!
Of course when you try an remount, it doesn't get recognised by the system. If you unplug the drive and plug it into another mac that didn't use it when it crashed (macbook on 10.6.8) once that drive has read and it and "Sees" all the files, when you plug it back in to the other machine everything goes back to normal, until a machine nods off that is.
Apple must have tried a correction with 10.8.2 as the USB 2 drives are fine now.
I know I given you no fix here, but I think we need to pool information.
Regards, Image F/X