A Flexible Garbage Collect Algorithm for Flash Storage Management

Log-structured file system (LFS) is widely used in multimedia terminals, which always use flash memory as main storage. Flash memory must be erased before writing and the maximum erasure times of each block is limited, therefore, the flash storage management is quite different from other storages. A flash storage system requires a garbage collect and cleaning mechanism to reclaim the invalidated space for future use. An efficient garbage collect algorithm should achieve wear leveling with low cleaning cost, but cleaning cost and wear levering are two conflicting objectives. Efficient cleaning always comes along with wear skewness, since the blocks (maybe 80% of capacity) with cold data are expected to be seldom erased to decrease total erasure count, while the blocks with hot data will reach the erasure limitation soon, which is caused by frequent accessing.In this paper, a flexible garbage collect algorithm is proposed to achieve an un-absolute balance, since different flash life phase needs different optimization. It is quite wise to go in for low cleaning cost when the flash is fresh, but when it is nearly worn out, wear leveling is more important.