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Unformatted text preview: s physical storage location changes.
• Better file abstraction.
• ~jon– used to be stored on machine M1 now on M2
• Separates the naming hierarchy form the storage-devices
Remote File Access
Reduce network traffic by retaining recently accessed disk blocks
in a cache, so that repeated accesses to the same information
can be handled locally.
• If needed data not already cached, a copy of data is brought from
the server to the user. Usually grab a large chunk.
• Accesses are performed on the cached copy.
• Files identified with one master copy residing at the server
machine, but copies of (parts of) the file are scattered in different
• Cache-consistency problem – keeping the cached copies
consistent with the master file. Cache
Cache Update Policy
Write-through – write data through to disk as soon as they are placed
on any cache. Reliable, but poor performance.
Delayed-write – modifications written to the cache and then written
through to the server later. Write accesses complete quickly; some
data may be overwritten before they are written back, and so need
never be written at all.
• Variation – scan cache at regular intervals and flush blocks that have
been modified since the last scan. Typical.
• Variation – write-on-close, writes data back to the server when the
file is closed. Best for files that are open for long periods and
frequently modified. Andrew File System (AFS). Consistency
Is locally cached copy of the data consistent w...
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- Summer '14
- Operating Systems