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    SubjectRe: Memory upgrade: not faster / nfs
    Christoph Trautwein wrote:
    >
    > Problem:
    > ! NFS is a filesystem. Filesystems are not cached.
    > ! The only thing that's cached in UN*X are block
    > ! devices. This is the wrong place to cache.
    [...]
    > Questions:
    > Is it correct how I see these things?
    > Why are filesystems not buffered?
    > Is there a nfs implementation that does buffering?

    They are not buffered due to a lack of protocols which recognices
    changes in the remote filesystem. A protocol which transfers all
    changes in files may slow down the system dramatically, if

    - the client is not as fast as the server
    - the connection is very slow
    - many clients using a server, all changes then must be transfered
    vise versa

    Furthermore this would cause a load on the client even it is not used.

    My suggestions to solve this really nasty problem are the following:

    - only on one client used filesystems (not used by the server)
    could be cached (rarely used)
    - caching of read only filesystems is possible (splitting into read
    only part eg. /usr/* and a read-write part)
    - introduce an cache protocol, working this way:

    - whenever the client opens a file for reading, first there is
    searched in the clients cache
    - if found, the file dates are compared over network
    - if equal use the clients cache
    - if not transfer from server
    - if not, transfer from server

    - whenever the client opens a new file for writing, transfer
    while closing
    - whenever a file on the server is opened for appending or
    read-write go the same way as opening for reading, transfer
    it back while closing

    ....................DK
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