Bizarre Problem with Laptop Drive

[Flames Fan, Ph.D.]

So I've had a very weird thing happen twice now under near identical conditions, and hope the minds here can help.

I have a mid-2009, 15 inch Macbook Pro. A few months ago, I figured the stock hard drive had been getting on in age and replaced it with a 500 gb WD Scorpio Black. I used SuperDuper to make the Scorpio a clone of the original hard drive, and put the old drive in an external enclosure to use as a backup drive.

So then I got the itch, and a month later bought a 120 gb OWC Mercury Extreme Pro 3G SSD. Using SuperDuper again, I made the SSD a startup disk with the applications on it, and using a data doubler, I placed the Scorpio Black into the optical bay to hold all of my files, including music.

So basically, my computer runs off the SSD, and fetches files from the HD. On two occasions now, while listening to music (iTunes running off SSD, music files on HD), I've had the mounted HD simply unmount and disappear. The computer doesn't freeze, but the programs with files loaded simply put up notices that the file is no longer available. iTunes hangs for a while and eventually puts up an error dialogue. One time, iTunes was streaming to an Airport Express, and the other time streaming to an Apple TV 2nd gen.

Both times when this happened, I shut down and rebooted, but the HD didn't show back up. Both times I figured something had wiggled loose, so I opened the computer up and checked the connections, but nothing appears loose / disconnected. After verifying the connections, I reboot and the HD remounts as if nothing happened.

Any clues? I feel it's a software thing, because both times that the HD has unmounted, it's been when the computer is just stationary and running; ie. it hasn't been bumped / dropped. I really don't think it is the connections because they're very stable and not the type of thing to "loosen". Is there a meaningful way that I can diagnose this?

[sclitheroe]

Have you tried disabling all drive-related power saving options in System Preferences?

If that doesn't work, I would also try disabling the sudden motion sensor (I know you say it isn't getting bumped, however, OS X isn't expecting ANY motion reporting from the optical SATA channel, so maybe it gets confused)

In Terminal, you can disable the Sudden Motion Sensor by typing sudo pmset -a sms 0 and pressing Return (changing the setting to a zero disables the module).


Edit: I'm not suggesting this is going to fix the problem, but we can see if it changes the behavior, which will help isolate the problem.