SSD unmounts randomly

I have the exact same issue, the SSD (Evo 840) is installed into the Superdrive Bay and after about 3 + hours it'll unmount and since it's my boot drive. the symptoms are exactly what you'd expect, anything that needs to access the SSD will indefinitely pause, until I restart. The SSD came from a different laptop and was working perfectly and my other HDD inside doesn't have the same issue.

Macbook Pro 2012 Yosemite

8GB 1600Mhz

The IO errors cause a kernel panic.

19/03/2015 11:46:01.000 am kernel[0]: Limiting closed port RST response from 359 to 250 packets per second

19/03/2015 11:46:07.000 am kernel[0]: disk0s2: I/O error.

19/03/2015 11:46:24.000 am kernel[0]: disk0s2: I/O error.

19/03/2015 11:46:34.737 am nsurlstoraged[228]: Error: stepSQLStatement:toCompletionWithRetry - stepping returned unhandled result=11, DB=/Users/joshuawaring/Library/Caches/com.apple.Safari/Cache.db

19/03/2015 11:46:36.000 am kernel[0]: disk0s2: I/O error.

19/03/2015 11:49:59.000 am bootlog[0]: BOOT_TIME 1426736999 0

If you are getting I/O errors, the hard drive may be failing. Do a backup, preferable 2 separate ones on 2 drives. Boot to the Recovery Volume (command - R on a restart or hold down the option/alt key during a restart and select Recovery Volume). Run Disk Utility Verify/Repair and Repair Permissions until you get no errors. Restart and test.

So to update what I've done since my last update,

I decided to eliminate that SSD, I have 3 Evo's lying around the place in computers so I swapped one out for the one inside the MBP.

A different Evo had the exact same issue as before with it powering down while in use (I even got a message saying I should eject first), at the time I was using carbon copy to clone from a external HDD which I'd booted from onto the new Evo.

The old one which was originally showing errors in now running in my Windows Desktop with no issues or signs of failure.

Also I've tested both SATA ports, with a HDD Caddy and the power down is present from both ports which rules out the SATA cable.

What I'm left with is no problem with the SATA cable and no issue with the SSD, as I'm currently running off a spare HDD I found and put into the MBP which has no issues so that rules out a problem with power delivery. I'm left with a problem with Compatibility, There was a firmware update late last year which was released after most of the posts have been made about no problems with the Evo, or a Failing controller that can't handle SATA III as all of the drives I've used are SATA II.

On a final note I notice it tends to power down after writing large amounts of data as it turned off most frequently when installing or cloning (After about 20GB). although ran with no issued for 3 hours with general use.

If you live near an Apple Store, make a Genius Bar appointment to have the computer tested. Supposedly there is no charge for testing. Use 2nd link if not near an Apple Store or aren’t in the US. Hardware Repair - Keeping Confidential Data Safe

Genius Bar Reservation US

Authorized Service Provider

Sadly it's been before and the day I bought it (last week) the person took it to the Apple Store and said they couldn't detect any issues, although he knew some existed due to extreme load times and stalling which is why I got it so cheap ($400 AU) which all was solved with a new HDD, but that's a whole other can of beans with the HDD benchmarking fine, but performing horribly.

The HDD (Not the original) is running rather well speed wise so I might just ditch my plans for a SSD 😟

I'll try a few more things and then consider getting a 250GB SSD of a different brand or just sticking with the HDD