Re: Link performance over NFS degraded in RHEL5. -- was : Read/Write NFS I/O performance degraded by FLUSH_STABLE page flushing

Brian R Cowan
2009-06-05T13:03:14Z

Personally, I would leave the default export options alone. Simply because
they more or less match the defaults for the other NFS servers.

Also, there may be negative impacts of changing the default export option
to no_wdelay on really busy servers. One possible result is that more CPU
time gets spent waiting on writes to disk.

I'm a bit paranoid when it comes to tuning *server* settings, since they
impact all clients all at once, where client tuning generally only impacts
the one client.

=================================================================
Brian Cowan
Advisory Software Engineer
ClearCase Customer Advocacy Group (CAG)
Rational Software
IBM Software Group
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From:
Trond Myklebust <trond.myklebust@fys.uio.no>
To:
Steve Dickson <SteveD@redhat.com>
Cc:
Neil Brown <neilb@suse.de>, Greg Banks <gnb@fmeh.org>, Brian R
Cowan/Cupertino/IBM@IBMUS, linux-nfs@vger.kernel.org
Date:
06/05/2009 08:48 AM
Subject:
Re: Link performance over NFS degraded in RHEL5. -- was : Read/Write NFS
I/O performance degraded by FLUSH_STABLE page flushing

On Fri, 2009-06-05 at 07:35 -0400, Steve Dickson wrote:
> Brian R Cowan wrote:
> > Trond Myklebust <trond.myklebust@fys.uio.no> wrote on 06/04/2009
02:04:58
> > PM:
> >
> >> Did you try turning off write gathering on the server (i.e. add the
> >> 'no_wdelay' export option)? As I said earlier, that forces a delay of
> >> 10ms per RPC call, which might explain the FILE_SYNC slowness.
> >
> > Just tried it, this seems to be a very useful workaround as well. The
> > FILE_SYNC write calls come back in about the same amount of time as
the
> > write+commit pairs... Speeds up building regardless of the network
> > filesystem (ClearCase MVFS or straight NFS).
>
> Does anybody had the history as to why 'no_wdelay' is an
> export default? As Brian mentioned later in this thread
> it only helps Linux servers, but that's good thing, IMHO. ;-)
>
> So I would have no problem changing the default export
> options in nfs-utils, but it would be nice to know why
> it was there in the first place...

It dates back to the days when most Linux clients in use in the field
were NFSv2 only. After all, it has only been 15 years...

Trond