[NFS] New version of Linux NFSv3 client is out...

[Markus Stenberg]

Trond Myklebust <trond.myklebust en fys.uio.no> writes:
> >>>>> " " == David S Miller <davem en redhat.com> writes:
>      >    From: Trond Myklebust <trond.myklebust en fys.uio.no> Date: 25
>      >    Jan 2000 09:55:55 +0100
> 
>      >    Please note that the knfsd server has consistently violated
>      >    this part of the NFSv2 protocol: knfsd acknowledges a write
>      >    statement from the client without ensuring that data has
>      >    been flushed to disk, thus the client is not guaranteed that
>      >    anything it has written will survive a server failure.
> 
>      > Come again?  I see a nfsd_sync and a write_inode_now there in
>      > the knfsd write paths.
> nfsd_sync is only called if the write gathering code is enabled
> (which is never the case at the moment).
> 
> You have to explicitly set the 'sync' option in /etc/exports in order
> for the write_inode_now() stuff to be called.
> 
> Hence, the default behaviour is to violate the NFSv2 protocol.

Nod, and that isn't very good. Although violating NFSv2 protocol _has_ to
be done if you want to guarantee any(*) performance, it's still bad idea as
default behavior.

> 
> Cheers,
>   Trond

-Markus

(*) On HP-(S)UX, the default behavior is standard-based and there is
async-writes option. Between HP-(S)UXes, performance increase is roughly
10-fold between sync<>async. I haven't tried it with Linux, but I expect
results to match.

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