With the emergence of Storage Networking, distributed file systems that allow data sharing through shared disks will become vital. We refer to Cluster File Systems as a distributed file systems optimized for environments of clustered servers. The requirements such file systems is that they guarantee file systems consistency while allowing shared access from multiple nodes in a shared-disk environment. In this paper we evaluate three approaches for designing a cluster file system - conventional client/server distributed file systems, symmetric shared file systems and asymmetric shared file systems. These alternatives are considered by using our prototype cluster file system, HAMFS (Highly Available Multi-server File System). HAMFS is classified as an asymmetric shared file system. Its technologies are incorporated into our commercial cluster file system product named SafeFILE. SafeFILE offers a disk pooling facility that supports off-the-shelf disks, and balances file load across these disks automatically and dynamically. From our measurements, we identify the required disk capabilities, such as multi-node tag queuing. We also identify the advantages of an asymmetric shared file system over other alternatives.

Unix’s lack of a robust and expandable file system has become a significant problem with the growth of UNIX in large commercial environments. The HAMFS (Highly Available Multi-server File System) is a cluster file system designed to address this need. HAMFS offers disk-pooling, supports off-the-shelf disks, and automatically balances file load across disks dynamically. Data residing in a disk pool is directly accessible from every node in a HAMFS cluster. As user’s capacity requirements grow, HAMFS provides easy disk pool expansion. Finally, HAMFS provides uniform scaling of file system performance from a single node configuration to large multi-node clusters, offering significant performance advantage over traditional file systems. For example, in short file access situations, HAMFS provide a factor of five performance improvement over NFS, and a factor of two improvement over conventional local file systems. Technologies developed for HAMFS are applied to Fujitsu’s file system product SafeFILE. 1.