A couple of weeks ago we already reported that the Samsung 840 EVO SSDs are still experiencing slow read speeds with old data. basically TechReport placed a couple of SSDs on shelf, didn't use them. Then after three months they connected them again and boom, slow performance of the old data written.

The issue was supposedly fixed with a firmware update (EXT0CB6Q-firmware) issued in October, but some patched drives continue to exhibit the problem, including one of our own. Late Friday afternoon, Samsung issued the following statement on the matter:

In October, Samsung released a tool to address a slowdown in 840 EVO Sequential Read speeds reported by a small number of users after not using their drive for an extended period of time. This tool effectively and immediately returned the drive’s performance to normal levels. We understand that some users are experiencing the slowdown again. While we continue to look into the issue, Samsung will release an updated version of the Samsung SSD Magician software in March that will include a performance restoration tool.

If you look at the screenshot above you can see the performance degraded. This test unit 840 EVO SSD spent more than three months of the shelf, he results are pretty shocking: the months old data on the disk was only recoverable with an average read speed of 35.1MB/s. 

After formatting the disk and loading it with new data the disk averaged 430MB/s in HD Tach, there's a abvious issue with long-term degradation of data stored in the triple-bit-per-cell memory.

Samsung investigating 840 EVO slowdowns