Software - Practice & Experience, 21(12), pp. 1289-1299, 1991
Abstract:
This paper describes a general-purpose file system that uses a
write-once-read-many (WORM) optical disk accessed via a magnetic disk
cache. The cache enables blocks to be modified multiple times before
they are written to the WORM and increases performance. Snapshots of
the file system can be made at any time without limiting the users'
access to files. These snapshots reside entirely on the WORM, are
accessible to the user via a second read-only file system, do not
contain multiple copies of unchanged data, and can be used to rebuild
the file system in the event that the disk cache is destroyed. The
file system has been implemented as part of Plan 9, an experimental
operating system under development at AT&T Bell Laboratories.