Phoenix: A low-power fault-tolerant real-time network-attached storage device

Phoenix is a real-time network-attached storage device (NASD) that guarantees real-time data delivery to network clients even across single disk failure. The service interfaces that Phoenix provides are best-effort/real-time reads/writes based on unique object identifiers and block offsets. Data retrieval from Phoenix can be serviced in server push or client pull modes. Phoenix's real-time disk subsystem performance results from a standard cycle-based scan-order disk scheduling mechanism. However, the disk I/O cycle of Phoenix is either completely active or completely idle. This on-off disk scheduling model effectively reduces the power comsumption of the disk subsystem, without increasing the buffer size requirement. Phoenix also exploits unused disk storage space and maintains additional redundancy beyond the generic RAID5-style parity. This extra redundancy, typically in the form of block replication, reduces the time to reconstruct the data on the failed disk. This paper describes the design, implementation, and evaluation of Phoenix, one of the first, if not the first, NASDs that support fault-tolerant, real-time, and low-power network storage service.