Samsung issued a firmware fix for EVO 840 SSD slowdown issues when reading old data but reports are still coming in on forums and some tech websites that the performance issues are still occurring. The Tech Report writes Samsung is acknowledging the issue and promises to release another fix:
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.
We hope this will resolve the issue but remain skeptical about the long-term performance of the TLC memory used in these disks. On a related note, a large number of people claim the performance issues occur on the regular 840 SSDs as well, but Samsung has yet to acknowledge the issue exists on the non-EVO 840s.