Integrating the Spiralog file system into the OpenVMS operating system
Mark A. Howell, Julian M. Palmer · 1996
this paper deals with the approach to integrating a new file system into the OpenVMS environment and preserving application compatibility. It describes the various levels at which the file system could have been integrated and the decision to emulate the low-level file system interface. Techniques such as tracing, source code scanning, and functional analysis of the Files-11 file system helped determine which features should be supported by the emulation. The Spiralog file system uses extensive write-back caching to gain performance over the write-through cache on the Files-11 file system. Applications have relied on the ordering of writes implied by writethrough caching to maintain on-disk consistency in the event of system failures. The lack of ordering guarantees prevented the implementation of such careful write policies in write-back environments. The Spiralog file system uses a write-behind cache (introduced in the Echo file system) to allow applications to take advantage of write-back caching performance while preserving careful write policies.