Storage Management Method for Hybrid Storage System to Reduce Extent Fragmentation

Abstract

A hybrid storage system consists of a small and fast solid state drive (SSD) and one or more slow and large hard disk drives (HDD). The purpose of a hybrid storage sys-tem is to exploit the IO performance of SSDs to enhance the overall IO performance with comparatively low cost. In a hybrid storage system, since the size of a SSD is small, the storage utilization for the SSD is very important to guarantee the performance of a hybrid storage system. Some existing hybrid storages use extents to manage a large storage efficiently. However, they cause an extent fragmentation problem. The extent fragmentation reduces the SSD utilization and the overall performance of a hybrid storage system. In this paper, to solve the problem we propose a new mapping method that uses different size of IO unit for SSD and HDDs. Also, we perform simulations to show that our proposed method guarantees better SSD utilization than existing methods.