AFRAID - A Frequently Redundant Array of Independent Disks

Disk arrays are commonly designed to ensure that stored data will always be able to withstand a disk failure, but meeting this goal comes at a significant cost in performance. We show that this is unnecessary. By trading away a fraction of the enormous reliability provided by disk arrays, it is possible to achieve performance that is almost as good as a non-parityprotected set of disks. In particular, our AFRAID design eliminates the smallupdate penalty that plagues traditional RAID 5 disk arrays. It does this by applying the data update immediately, but delaying the parity update to the next quiet period between bursts of client activity. That is, AFRAID makes sure that the array is frequently redundant, even if it isn't always so. By regulating the parity update policy, AFRAID allows a smooth trade-off between performance and availability. Under real-life workloads, the AFRAID design can provide close to the full performance of an array of unprotected disks, and data availabili...

• Type: Conference
• Year: 1996
• Where: USENIX
• Authors: Stefan Savage, John Wilkes
• Keywords: AFRAID Design, Disk Arrays, Operating System, RAID 5, USENIX 1996