Swift/RAID: A Distributed RAID System

The Swift VO architecture is designed to provide high data rates in support of multimedia type applications in general-purpose distributed environments through the use of distributed striping. Strþing techniques place sections of a single logical data space onto multiple physical devices. The original Swift prototype was designed to validate the architecture, but did not provide fault tolerance. We have implemented a new prototype of the Swift architecture that provides fault tolerance in the distributed environment in the same manner as RAID levels 4 and 5. RAID (Redundant Arrays of Inexpensive Disks) techniques have recently been widely used to increase both performance and fault tolerance of disk storage systems. The new Swift/RAID implementation manages all communication using a distributed transfer plan executor which isolates all communication code from the rest of Swift. The transfer plan executor is implemented as a distributed finite state machine that decodes and executes a set of reliable data-transfer operations. This approach enables us to easily investigate alternative architectures and communications protocols. Supported in part by the National Science Foundation under Grant NSF CCR-9111220 and by the Office of Naval Research under Grant N00014-92-J-1807 @ 1994 The USENIX Association, Computing Systems, Vol. 7 . No. 3 . Summer 1994 333 Providing fault tolerance comes at a cost, since computing and administering parity data impacts Swiff/RAID data rates. For a five node sysÛem, in one typical performance benchmark, Swift/RAID level 5 obt¿ined 87 percent of the original Swift read throughput and 53 percent of the write throughput. Swift/RAID level 4 obtained 92 petcent of the original Swift read throughput and 34 percent of the write throughput.