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-statemen...
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-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/pr...
Samsung has some firmware updates and software utilities that should be able to restore the performance of your SSD's.