IF YOU OWN A SAMSUNG EVO OR EVO PRO, 840 OR 850, be sure to install the latest firmware before turning on TRIM support
There is a lot of confusion about the multiple issues with the Samsung and the need for firmware update. Some users are insisting the problem is only with Linux, and you don't need a firmware update. Not true, there are actually TWO critical issues discovered so far with the EVO drives, one Linux related, the other NOT.
One problem, related to the drives having an incorrect bit set that tells the OS what type of NCQ queing command it supports. The incorrect bit says that EVO supports beyond normal sequential queued TRIM commands (it does not) and then Linux attempts to implement (which does support more than sequential) and runs in to problems.
Windows and OS X ignore this bit because as of now, they only support 'normal' sequential TRIM, so is unaffected BY THIS ONE PARTICULAR PROBLEM.
HOWEVER, there is ANOTHER issue with Samsung EVO related to reading data that is 'old' (not been accessed for a long time) where the charge may degrade, requiring multiple attempts to read the data. This problem is not OS specific and deals with the actual physical nature of the drive itself. The latest firmware from April 15, 2015 fixes this by periodically 'refreshing' in the background all the data on the drive to keep the charge strong, even data that isn't accessed. This problem affects the drive regardless of OS, so highly recommended you update the firmware. Read more about this SEPARATE PROBLEM UNRELATED TO THE LINUX PROBLEM HERE:
Firmware update is provided as an ISO bootable CD image that will boot Macs or Windows PC., using a Linux micro kernel, that locates and updates the drive. I've updated without issues.
As for all the conspiracy theories about why Apple did not enable trim support for non Apple branded SSDs, until now, this is a perfect example. Apple no doubt tested all kinds of brands and manufacturers when deciding who to use in their own machines, and likely found that many had bugs in their implementation TRIM. This has been confirmed now in early drives using Sandforce controllers in which live data could be incorrectly marked and deleted by using TRIM. Apple did not want people turning on TRIM with other drives, and then be accused of data loss or issues which were outside of their control, and be BLAMED for it, as people would automatically assume based on their experience with rotational drives that 'it can't be the drive, it must be Apple'. BAM ! Class action suit. So after testing and finding out the brands they would NOT use in their machines, Apple decided the safe approach was only enable TRIM on the drives that passed their testing. Publicly, Apple would never issue a list of BAD drives; that's not their responsibility, and they have complex relationships with component manufacturers they have to protect. Company X may have a bad SSD that Apple won't use, but it still buys memory chips from X, for example.
To that point (that some SSDs brands are not fault free or were not early on) here it is mid 2015 and even a brand as popular as Samsung EVO, we're still discovering issues. If you have an older drive with a Sandforce controller, you may want to consider upgrading too. Note that OWC which sells SSDs using Sandforce controllers, from day one tried to convince everyone their drives didn't need TRIM (bogus)....well now we kind of know why they were saying that. Amazing how their marketing turned what was a undisclosed bug into a reason to buy the product.