A High Performance and Reliable Hybrid Host Cache System

Modern date centers widely use network storage systems as shared storage solutions. Storage server typically deploys the redundant array of independent disks (RAID) technique to provide high reliability, e.g., RAID5/6 can tolerate one/two disk failures. Compared with traditional hard disk drives (HDDs), solidstate drives (SSDs) have lower access latency but higher price. As a result, clientside SSDbased caching has gained more and more popularity. Writeback policy can significantly accelerate the storage I/O performance, however, it fails to ensure date consistency and durability under SSD failures. Writethough policy simplifies the consistence model, but fails to accelerate the write accesses. In this paper, we design and implement a new hybrid host cache (HHC). HHC selectively stores mirrored dirty cache blocks into HDDs in a logstructured manner, and utilizes the write barrier to guarantee the data consistency and durability. Through reliability analysis, we show that the HHC layer has much longer mean time to data loss (MTTDL) than the corresponding backend storage array. In addition, we implement a prototype of HHC and evaluate its performance in comparison with other competitors by using Filebench. The experimental results show that under various workloads, HHC achieves comparable performance compared with the writeback policy, and significantly outperforms the writethrough policy.