ISM- An Intra-Stripe Data Migration Approach for RAID-5 Scaling

Scaling is often carried out in modern RAID systems to meet the ever increasing demand of storage capacity and I/O performance. However, the scaling process of RAID-5 system is not trivial, due to its specific data/parity layout. Previous approaches of RAID-5 scaling require either migrating almost all data blocks in the system, or recalculating all or some of the parity blocks during scaling. This paper proposes a new RAID-5 scaling approach called ISM (Intra-Stripe Migration). With ISM, data migrations only happen within stripes, which means that the coding relationship among blocks remains the same. Therefore, the parity blocks do not need to be recalculated after data migration, which greatly reduces the I/O and computational costs. The properties of ISM approach can be summarized as follows: (1) it requires the minimum amount of data blocks to be migrated, (2) it supports data migration without recalculating parity blocks, and (3) it supports multiple successive scaling operations while keeping the above properties. The simulation results on DiskSim show that: (1) ISM reduces the scaling time from 47.91% to 87.01% and from 88.94% to 96.58% compared with GSR and ALV respectively in offline scaling, (2) under two real-world I/O traces, ISM also outperforms GSR by 64.15% to 87.30%, and ALV by 92.38% to 95.98% in scaling time, and (3) ISM maintains almost the same performance of data access with ALV and GSR after scaling.