Michael Weiser <M.Weiser@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > quick question: Is there any support for write caching on NFS{,v4} yet?
> > No, not yet.
>
> Is there work being done on it, perhaps even an ETA?
Not at the moment. It's not particularly difficult to implement simply. The
problem is one of cache coherency. If you make a write to the NFS server, how
do you know that your write hasn't hidden someone else's write that was
performed immediately before? With NFS2/3 the only consistency data you have
is the mtime, ctime and filesize. NFS4 adds further information, but I'm not
sure how useful it actually is.
AFS gets around this by having a "data version number" - a number incremented
for each write committed to the file. You get this back in response when you
issue an FSSTOREDATA op, and if it's not one more than the number you had
previously, you have to invalidate your cache.
This is also a problem for the pagecache with NFS, it's just that having a
persistent cache for NFS makes the problem persistent too.
David
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