StRAID: Stripe-threaded Architecture for Parity-based RAIDs with Ultra-fast SSDs

Popular software storage architecture Linux Multiple-Disk (MD) for parity-based RAID (e.g., RAID5 and RAID6) assigns one or more centralized worker threads to efficiently process all user requests based on multi-stage asynchronous control and global data structures, successfully exploiting characteristics of slow devices, e.g., Hard Disk Drives (HDDs). However, we observe that, with high-performance NVMe-based Solid State Drives (SSDs), even the recently added multi-worker processing mode in MD achieves only limited performance gain because of the severe lock contentions under intensive write workloads.

In this paper, we propose a novel stripe-threaded RAID architecture, StRAID, assigning a dedicated worker thread for each stripe-write (one-for-one model) to sufficiently exploit high parallelism inherent among RAID stripes, multi-core processors, and SSDs. For the notoriously performance-punishing partial-stripe writes, StRAID presents a two-phase stripe write mechanism to opportunistically aggregate stripe-associated writes to minimize write I/Os; and designs a parity cache to reduce write-induced read I/Os on parity disks. We evaluate a StRAID prototype with a variety of benchmarks and real-world traces. StRAID is demonstrated to consistently outperform MD by up to 5.8 times in write throughput without affecting the read performance.