A Distributed Storage System with Dynamic Tiering for iSCSI Environment

In this paper, we propose a distributed storage system which relocates data blocks autonomously among the storage nodes. In the system which is composed of heterogeneous storage nodes, there are performance gaps among the storage devices. The storage tiers are made by such gaps in the system. When frequently accessed data blocks are placed on improper storage tier, system performance may decline. To avoid this problem, a system administrator should periodically investigate the state of storage utilization and relocate the data blocks to the proper node. Although this makes efficient use of storage devices, administrators' workload is quite heavy. Our system is aimed at the realization of the following two functions, (i) Run-time construction of the storage tiers from the storage devices, and (ii) Automated block migration among the tiers. In general, such high level management tends to bring unignorable overhead. We also show a technique to reduce management traffic in iSCSI environment.