A memory hierarchy-aware metadata management technique for Solid State Disks

Abstract

Solid State Disk (SSD) drives are rapidly replacing conventional hard disk drives (HDDs) due to their remarkable performance gains. For emulating HDDs, SSDs require a flash translation layer (FTL) which hides the out-of-place-update feature of NAND flash memories. In the latest large-capacity SSDs, FTLs must manage huge metadata such as a logical-to-physical address mapping table, a pool of free blocks, or a list of garbage blocks with their erase counts. The total metadata cannot reside on a small on-chip SRAM so that it must be hierarchically distributed in DRAM or NAND flash memories. This paper presents an efficient metadata management technique for SSDs which fully exploits memory hierarchy of an SSD. By the proposed technique, the distributed metadata can be efficiently searched or updated with small overheads. Experimental results show that overheads of metadata management become considerably large in the latest SSDs and they are minimized efficiently by the proposed technique.