Combined data caching and delayed parity update in RAID with SSD cache

Hybrid storage that uses SSD over disk-based RAID is usual in enterprise environments. One way to exploit an SSD over RAID is using it as data cache and another is using it as LeavO cache that reduces parity update overhead of RAID. In this paper, we combine data caching and LeavO caching schemes and identify optimal cache sizes. To do that, we derive cost models of combined data and LeavO caching. Also, we propose Adaptive LeavO Cache that dynamically adjusts data cache and LeavO cache sizes for evolving workloads. The experiments show that the Adaptive LeavO Cache performs far better than conventional data caching scheme and on a par with the off-line optimal scheme that determines optimal sizes after exploring all possible sizes of data cache and LeavO cache.