An anonymous reader writes with a link to TechSpot's explanation of the reason behind the performance degradation
noticed by many purchasers of certain models of Samsung SSD (the 840 and 840 EVO), and an evaluation of the firmware updates that the firm has released to address is. From the piece, a mixed but positive opinion of the second and latest of these firmware releases: "It’s not an elegant fix, and it’s also a fix that will degrade the lifetime of the NAND since the total numbers of writes it’s meant to withstand is limited. But as we have witnessed in Tech Report’s extensive durability test there is a ton of headroom in how NAND is rated, so in my opinion this is not a problem. Heck, the Samsung 840 even outlasted two MLC drives.
As of writing, the new firmware has only been released for the 2.5” model of the SSD 840 EVO, so users of the 840 EVO mSATA model still have to be patient. It should also be noted that the new firmware does not seem to work well with the TRIM implementation in Linux, as this user shared how file system corruption occurs if discard is enabled."