Parity Resynchronization using a Block-level Journaling for Software RAID

Software redundant arrays of independent disks (RAID) suffer from several hours of resynchronization time after a sudden power-off. Data blocks and a parity block in a stripe must be updated in a consistent manner. However, a data block may be updated without a parity update if power goes off. Such a partially modified stripe must be updated with a correct parity block after a reboot. It is difficult, however, to find which stripe is partially updated. The widely used traditional parity resynchronization approach entails a very long process that scans the entire volume to find and fix partially updated stripes. As a remedy to this problem, this paper presents a parity resynchronization scheme that exhibits a small overhead for a wide range of workloads, finishes parity resynchronization within several minutes, and is transparent to file systems, thanks to a new seamless block-level journaling. The proposed scheme is integrated into a software RAID driver in a Linux system. A performance evaluation demonstrates that the proposed scheme shortens the resynchronization process from 200 min to 30 s with 1% overhead, compared to 51% overhead for the prior scheme.