△FTL: Improving SSD Lifetime via Exploiting Content Locality

摘要

NAND flash-based SSDs suffer from limited lifetime due to the fact that NAND flash can only be programmed or erased for limited times. Among various approaches to address this problem, we propose to reduce the number of writes to the flash via exploiting the content locality between the write data and its corresponding old version in the (lash. This content locality means, the new version, i.e., the content of a new write request, shares some extent of similarity with its old version. The information redundancy existing in the difference (delta) between the new and old data leads to a small compression ratio. The key idea of our approach, named AFTL (Delta Flash Translation Layer), is to store this compressed delta in the SSD, instead of the original new data, in order to reduce the number of writes committed to the flash. This write reduction further extends the lifetime of SSDs due to less frequent garbage collection process, which is a significant write amplification factor in SSDs. Experimental results based on our AFTL prototype show that AFTL can significantly reduce the number of writes and garbage collection operations and thus improve SSD lifetime at a cost of trivial overhead on read latency performance.