CRAZNS: A Case for Conventional Namespace Support for RAID with ZNS SSDs
Published in 40th ACM/SIGAPP Symposium on Applied Computing (SAC '25), 2025
Recommended citation: Hangyul Kim, Inho Song, and Sam H. Noh. "CRAZNS: A Case for Conventional Namespace Support for RAID with ZNS SSDs." In Proceedings of the 40th ACM/SIGAPP Symposium on Applied Computing (SAC '25), pp. 1391–1398, Catania, Italy, March 2025. https://doi.org/10.1145/3672608.3707937 https://dl.acm.org/doi/10.1145/3672608.3707937
Hangyul Kim, Inho Song, and Sam H. Noh. 40th ACM/SIGAPP Symposium on Applied Computing (SAC ‘25), Catania, Italy.
Abstract
ZNS SSDs improve write performance by exposing sequential write pointers, but forbid in-place updates — which complicates building a RAID of ZNS devices since metadata and partial-parity logs are inherently update-heavy. CRAZNS adds a small conventional namespace to a ZNS RAID-5 and uses it to keep metadata and partial parity updateable. Compared to RAIZN (the state-of-the-art ZNS RAID), CRAZNS uses 4 GB of extra space for the conventional namespace but eliminates dedicated metadata zones (saving ~26 GiB), allows the maximum number of zoned namespaces, achieves 1.2× higher small-write throughput, and improves overall throughput by 1.1× by keeping more zones open concurrently.