New 840 EVO fix adds ''periodic refresh'' to firmware
 

Last year, some Samsung 840 EVO SSDs started exhibiting slower read speeds with old data. The problem was patched in October, but the fix didn't stick, with slowdowns returning months later. Samsung pledged to release another fix in March, and now, that update is scheduled for "later this month."

http://techreport.com/news/28112/new...sh-to-firmware