Disk space guarantees as a distributed resource management problem: a case study

In the single system UNIX, successful completion of a write system call implies a guarantee of adequate disk space for any new pages created by the system call. To support such a guarantee in a distributed file system designers need to solve the problems of accurately estimating the space needed, communication overhead, and fault tolerance. In the Calypso file system, which is a cluster-optimized, distributed UNIX file system, we solve these problems using an advance-reservation scheme. Measurements show that the overhead of this scheme for typical UNIX usage patterns is 1% to 3%.