The Tech Report revisits the Samsung 840 EVO SSD to check if the disk is still suffering from read speed slowdowns. Last year there was quite a controvert as enthusiasts discovered an issue that caused dramatic slowdowns when reading older data. Samsung issued a fix for an algorithmic error in the management routine that tracks the status of cells over time but The Tech Report's latest test doesn't bode well for the TLC drive.
In the chart below you can see the performance of The Tech Report's 840 EVO SSD which spent more than three months of the shelf before being called up for their new article. The results are quite 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 so it seems more and more that there's an issue with long-term degradation of data stored in the triple-bit-per-cell memory.
SSDs typically aren't left unpowered for months at a time, so it's possible that hiatus contributed to the slow read speeds exhibited by our sample. However, the other recent reports of read slowdowns come from drives that have been in service since the patch was applied. The issue doesn't appear to be confined to unused drives.