Re: nfs client: Now you see it, now you don't (aka spurious ESTALE errors)

[Larry Keegan <lk@pfw.demon.co.uk>]

On Tue, 6 Aug 2013 09:34:07 -0400
"J. Bruce Fields" <bfields@fieldses.org> wrote:
> On Tue, Aug 06, 2013 at 07:14:28AM -0400, Jeff Layton wrote:
> > On Tue, 6 Aug 2013 11:02:09 +0000
> > Larry Keegan <lk@pfw.demon.co.uk> wrote:
> > > These figures seem reasonable for a single SATA HDD in concert
> > > with dmcrypt. Whilst I expected some degradation from exporting
> > > and mounting sync, I have to say that I'm truly flabbergasted by
> > > the difference between the sync and async figures. I can't help
> > > but think I am still suffering from some sort of configuration
> > > problem. Do the numbers from the NFS client seem unreasonable?
> > > 
> > 
> > That's expected. Performance is the tradeoff for tight cache
> > coherency.
> > 
> > With -o sync, each write() sycall requires a round trip to the
> > server. They don't get batched and you can't issue them in
> > parallel. That has a terrible effect on write performance.
> 
> Note also mounting -osync and exporting with the "sync" export option
> are entirely different things.
> 
> The defaults are what you want (async mount option, sync export
> option) unless you've thought hard about it.  This is especially true
> on the server, since the "async" export option make it skip
> committing data to disk even when the protocol mandates it.

Righto. This makes sense. After a brief pause I'll see if I can tickle
the ESTALE problem under NFS 4.

With many thanks.

Yours,

Larry.