Xscale: Online X-Code RAID-6 Scaling Using Lightweight Data Reorganization

Disk additions to a RAID-6 storage system can simultaneously increase the I/O parallelism and expand the storage capacity. To regain a balanced load among both old and new disks, RAID-6 scaling requires moving certain data blocks onto newly added disks. Existing approaches to RAID-6 scaling are restricted by preserving a round-robin data distribution, and require migrating all the data, resulting in an expensive cost for RAID-6 scaling. In this paper, we propose Xscale, a new approach to accelerating X-code RAID-6 scaling by using lightweight data reorganization. Xscale minimizes the number of data blocks that require being moved, while maintaining a uniform data distribution across all disks. Furthermore, Xscale eliminates metadata updates while guaranteeing data consistency and data reliability. Compared with the round-robin approach, Xscale reduces the number of blocks to be moved by 63.689.5 percent, decreases the reorganization time by 35.62-37.26 percent, and reduces the I/O latency by 23.29-37.74 percent while the scaling programs are running in the background. In addition, there is no penalty in the performance of the data layout after scaling using Xscale, compared with the layouts maintained by other existing scaling approaches.