For those of you with a Samsung SSD 840 EVO SSD. Two weeks ago an issue occured that over time that the performance of the SSD crippled. Samsung now has a fixed the issue and released a new firmware as a solve.

Version EXT0CB6Q can be downloaded and and installed using Samsung SSD Magician software for Windows. It works on systems running on SATA AHCI host interfaces.

If you can not use Samsung SSD Magician software for whatever reasone, Samsung also has bade bootable disc images that you can use, these patch the drive without an active operating system. Obviously this is a big firmware update, so make sure you backup your files before applying it.

Update - alternatively try the new Performance Restoration tool (download)

Here's how Samsung describes the issue:

SSDs usually calibrate changes in the statuses of cells over time via the flash management software algorithm. Due to the error in the software algorithm, the 840 EVO performed read-retry processes aggressively, resulting in a drop in overall read performance. This only occurs if the data was kept in its initial cell without changing, and there are no symptoms of reduced read performance if the data was subsequently migrated from those cells or overwritten.

Samsung SSD 840 EVO Performance Restoration Software

Samsung is releasing a new firmware and performance restoration software package for the 840 EVO and 840 EVO mSATA. The firmware update is recommended to users who may have experienced any drop in read performance of the mentioned drives.

Running the software packages provided will first update the firmware(840 EVO : EXT0CB6Q, 840 EVO mSATA : EXT42B6Q), then scan and calibrate all existing data on the drive.

Note that the update time can be more than an hour depending on the amount of data.

Please wait for the firmware update to complete before starting any other operations.

For details, please refer to Samsung Performance Restoration v.1.0 Installation guide. Performance Restoration tool (download)