Preemptive Garbage Collection Scheme for the Response Latency Minimization of NAND Flash Memories

?????? ????????? ???????????? FTL??? ????????? ?????? ?????????????????? ????????? ?????? ???????????? ???????????????????????? ???????????? ??????????????? ???????????? ?????? ????????? ????????? ????????? ????????? ???????????? ????????? ????????? ??? ??????. ????????? ????????? ??????????????? ???????????? ????????? ?????? ??????????????? ???????????? ?????? ?????? ????????? ?????? ?????? ????????? ?????? ?????? ???????????? ??????????????? ???????????? ?????? ???????????? ???????????? ????????? ????????? ????????? ???????????? ??????. ????????? ????????? ????????? ???????????? ????????? ????????? ????????? ????????? ??????, ?????? ????????? ????????? ?????? ?????? ???????????? ?????? ???????????? ?????? ??????????????? ????????? ??? ??????. ??? ??????????????? ?????? ????????? ??????????????? ?????? ????????? ???????????? ???????????? ????????? ????????? ??????????????? ????????????. ???????????? ????????? ????????? ????????? ?????? ?????? ????????? ????????? ????????? ????????????, ?????? ????????? ???????????? ????????? ???????????? ????????????. ??? ????????? ???????????? ????????? ??????????????? ???????????? ????????? ????????? ?????? ?????? ????????? ?????? ????????? ???????????? ?????? ??????????????? ????????? ???????????? ???????????? ????????? ???????????? ???????????? ????????? ??????????????? ????????????????????? ?????????.Due to page re-mapping operations of FTLs, in NAND flash memory devices, the flash storage may suffer from a lack of capacity problem although the programmed pages are invalidated. Therefore, in order to sustain flash write performance and prolong the storage lifespan, the flash storage controller should conduct a garbage collection operation, whose goal is to physically eliminate invalid pages and collect valid pages from data blocks. However, the large number of page copy and block erase operations may cause a high response latency if the controller manages multiple number of garbage collection blocks. In this paper, we propose an efficient preemptive garbage collection mechanism. The preemptive garbage collection scheme uses a single block garbage collection operation by simply modifying the data structure of block map entries. The effectiveness of the proposed scheme is that the victim block selection overhead can be efficiently reduced; hence, the responsiveness to host requests is significantly improved