How to cut out expired data with nearly zero overhead for solid-state drives

Owing to flash memory constraints, a garbage collection (GC) mechanism hurts flash storage lifespan and performance since it generates a massive amount of write data to flash memory. To add insult to injury, all GC designs cannot identify disused data from valid data; therefore, all valid data, including disused data, will be rewritten to flash memory during the GC process. Fortunately, a flash storage vendor recently proposed a new write command to bring extra information to flash translation layer (FTL). Thanks to the new write command, the lifetime information of data can be brought from a host-side system to an FTL management layer for disused data identification. By such observations, this work proposes a dual-time referencing FTL (DTR-FTL) design to deal with disused data and minimize the overhead of GC by referring to data lifetime information and block retention time.