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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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