2LGC: An Atomic-Unit Garbage Collection Scheme with a Two-Level List for NAND Flash Storage

In NAND flash memory devices, pages marked “invalid” can remain in blocks and occupy flash space. Therefore, it is necessary to physically eliminate invalid pages and collect valid pages from the victim blocks in order to sustain flash write performance and storage lifespan. Although there have been many research studies on efficient garbage collection techniques, research has focused on victim selection methodologies and no solutions have been proposed for the victim selection process cost overhead. Indeed, the host system quite often suffers unendurable storage-access delays because garbage collection produces much computational over-head when doing victim selection. A novel garbage col-lection mechanism, called “Two-Level List-based Garbage Collection”, is proposed in this paper. The victim block selection overhead can be efficiently reduced in this scheme; hence, the responsiveness to host requests is significantly improved.