Cache Update Policy
- write data through to the master disk as soon as they are placed on any cache.
- Reliable, but poor performance.
- modifications written to the cache and then written through to the server later.
- Fast: some data may be overwritten before they are written back, and so need never be written at all.
- Poor reliability: unwritten data will be lost whenever a user machine crashes.
- Variations: write on close, update on regular intervals.