You aren't alone. The 840 and 840EVO were Samsung's first drives using 19nm planar TLC flash. With TLC flash they were storing 4 bits per flash cell, which at

You aren't alone. The 840 and 840EVO were Samsung's first drives using 19nm planar TLC flash. With TLC flash they were storing 4 bits per flash cell, which at that small process size gave all sorts of trouble with old, stale data. It was a pretty well documented problem: http://www.anandtech.com/show/8997/samsung-releases-statement-on-840-evo-performance-another-fix-is-in-the-works http://www.anandtech.com/show/8997/samsung-releases-statemen... The newer Samsung TLC drives use V-NAND, which supposedly has lower cell-to-cell interference due to the larger process size and 3D structure: http://www.samsung.com/global/business/semiconductor/html/product/flash-solution/vnand/overview.html http://www.samsung.com/global/business/semiconductor/html/pr... Samsung has some firmware updates and software utilities that should be able to restore the performance of your SSD's.