HS-BAS: A hybrid storage system based on band awareness of Shingled Write Disk

To increase the capacity of hard disk drive (HDD) with no significant cost, Seagate announced the world's first Shingled Write Disk (SWD) that employs Shingled Magnetic Recording (SMR) technology in 2014. The main drawback of SMR is that non-sequential write access to the disk is restricted due to overlap in the layout of data tracks. Seagate SWD mitigates these access restrictions by using an internal persistent cache (PCache). However, it encounters poor sustained non-sequential write performance due to high collection cost and low collection efficiency of its PCache, which makes it can only be used for backup/archive applications. In this paper, we propose a hybrid storage system HS-BAS to provide good sustained non-sequential write performance. In HS-BAS, we use SSD as the cache of SWD to reduce the effect of high collection cost of SWD PCache on system performance and implement three different cache collection policies based on band awareness of SWD to increase the collection efficiency of SWD PCache. Finally, our measurements on HS-BAS show that it provides superb sustained non-sequential write performance with a small capacity of SSD. For example, HS-BAS achieves 1.05 times and 0.26 times performance improvement compared with SWD and conventional HDD respectively for financial1 trace. By using conventional hybrid storage system Flashcache on SWD, we find that it only achieves little performance improvement and even worse performance in some traces. It is shown that HS-BAS performs better than Flashcache on SWD.