Reducing write amplification of DM-SMR disks by shingle-aware persistent cache

Shingled Magnetic Recording (SMR) Technology is a cutting edge disk tech that boosts areal density via overlapping track writing. However, track overlapping makes SMR devices unable to support in place updates on shingled tracks, risking data corruption and degrading random write performance. DM-SMR devices use an internal persistent cache to absorb writes and persist them later on in batches during garbage collection process to maintain compatibility. In this paper, we propose a new shingle aware persistent cache cleaning policy for DM-SMR drives. Unlike traditional management polices, our new policy first merges cached updates by flushing writes that can be safely written to the disk, i.e., in the shingle direction, so that the cache space can be freed without paying the cost of read-modify-write. In order to proactively free up more cache space, we adopted a delayed write back strategy, which detects the data blocks that can be safely written back to the disk and the write back order between them, thereby writing back more data at once. Our evaluations using several block I/O traces have shown that our persistent cache management policy delivers up to 2.31X better performance compared to the Skylight with a traditional set-associative baseline policy.