Parity Striping of Disk Arrays: Low-Cost Reliable Storage with Acceptable Throughput

An analysis of mirrored discs and of RAID5 shows that mirrors have considerably better throughput, measured as requests/second on random requests of arbitrary size (up to 1MB). Mirrors have comparable or better response time for requests of reasonable size (less than 100KB). But mirrors have a 100% storage penalty: storing the data twice. Parity striping is a data layout that stripes the parity across the discs, but does not stripe the data. Parity striping has throughput almost as good as mirrors, and has cost/GB comparable to RAID5 designs -combing the advantages of both for high-traffic disc resident data. Parity striping has additional fault containment and software benefits as well. Parity striping sacrifices the high data transfer rates of RAID designs for high throughput. It is argued that response time and throughput are preferable performance metrics. Outline Introduction Why Striping and RAID Are Inappropriate for OLTP Systems Parity Striping: Cheap Reliable Storage Plus High Throughput An Analysis of Mirrors, RAID5, and Parity Stripe Performance Mirrored Discs Parity Stripe Discs RAID5 Discs Applying the Analysis to a 10+2 array The Read-Only Case The Write-Only Case Analyzing a High-Performance Disc Other Benefits of Parity Striping Summary Acknowledgments References Appendix: Spreadsheets Corresponding to the Graphs