Date: 18 Aug 2000

Instant Image: Transitive and Cyclical Snapshots in Distributed Storage Volumes

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Abstract

Snapshots are a useful mechanism to manage data, particularly for backups in high-availability storage systems. This paper presents the Instant Image algorithm for handling snapshots of storage volumes in a distributed storage system. The algorithm places no restrictions on the choice of storage volumes, allowing snapshot relationships between storage volumes that can be transitive and cyclical. In addition, in a distributed environment with snapshot relationships involving n storage subsystems, reads and writes to storage volumes involve only O(1) storage subsystems per read or write, thereby reducing messaging costs. Finally, the algorithm is not specific to storage systems and can be applied to other contexts requiring snapshots. A performance analysis indicates doubling of average read and write performance on a cluster of storage subsystems.