Zebra: A Striped Network File System

This paper presents the design of Zebra, a striped network file system. Zebra applies ideas from log-structured file system (LFS) and RAID research to network file systems, resulting in a network file system that has scalable performance, uses its servers efficiently even when its applications are using small files, and provides high availability. Zebra stripes file data across multiple servers, so that the file transfer rate is not limited by the performance of a single server. High availability is achieved by maintaining parity information for the file system. If a server fails its contents can be reconstructed using the contents of the remaining servers and the parity information. Zebra differs from existing striped file systems in the way it stripes file data: Zebra does not stripe on a per-file basis; instead it stripes the stream of bytes written by each client. Clients write to the servers in units called stripe fragments, which are analogous to segments in an LFS. Stripe fragments contain file blocks that were written recently, without regard to which file they belong. This method of striping has numerous advantages over per-file striping, including increased server efficiency, efficient parity computation, and elimination of parity update. This paper will appear in the proceedings of the USENIX Workshop on File Systems, May 1992. This work was supported in part by the National Science Foundation under grant CCR-8900029, the National Aeronautics and Space Administration and the Defense Advanced Research Projects Agency under contract NAG2-591. Zebra April 28, 1992