XRAID Publicly Released As New RAID Implementation For XFS

Longtime Linux developer Christoph Hellwig today announced the initial public release of XRAID. XRAID is a declustered parity RAID implementation integrated into the XFS file-system. XRAID is focused on RAID for zoned XFS deployments. Hellwig explained of this new XRAID functionality for XFS: "The two primary aims of XRAID are to support parity RAID on zoned devices like SMR hard drives, and to provide a fast RAID implementation without inherent data integrity problems. XRAID, just like zoned XFS also works on conventional hard drives and SSDs. Optimizing for SSD performance has not been a focus, but even without that, writes are up to 20 times faster than mdraid. XRAID builds on the zoned allocator, which uses the RT subvolume to store file data separately from metadata, so that only file data is placed on sequential write required zones while metadata is stored on conventional devices or zones. XRAID takes advantage of this organization to only provide parity RAID for file data, where parity RAID works efficiently. Metadata redundancy is delegated to existing stacked Linux drivers like MD RAID mirroring, which is more suitable than parity RAID for small objects that are updated in place. The RAID implementation sits below the Zoned XFS I/O path, similar to a stacked block driver, and aggregates the physical zones of the underlying devices into logical zones that are used by the Zoned XFS as realtime groups. Declustered RAID describes a variant of RAID that distributes the D + P data and parity blocks in each stripe across a storage pool that contains more than D + P disks so that all disks participate in read, write and reconstruction operations and spare capacity is distributed over all disks. Declustered RAID provides much faster rebuild times than conventional RAID, and eases using of a large number of disks in a single storage pool. XRAID can rebuild to all devices that have spare capacity, and the rebuild order is dynamic, allowing to rebuild zones with multiple lost redundancies first, and rebuilding data zones before parity zones to reduce the overhead of degraded reads." XRAID has been in development for a year and a half. The initial public patches aren't yet ready for upstream submission but now at least at a stage for more testing and feedback. The kernel patches are out for review on the kernel mailing list. There is also a branch of the xfsprogs user-space programs for mkfs support with XRAID as well as a new "xraid" utility. Earlier this year Hellwig presented on the XRAID development and those interested can find his prior slides here. The performance of XRAID is looking good in the early benchmarks shown in that presentation.