Re: Problem: Clients freeze on transfer of large files, w gigabit lan

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Tue, 2010-06-29 at 07:45 +1200, Jasper Mackenzie wrote:
> >>     I and many others have been plagued by a problem that can be  
> >> summarised
> >> as follows:
> >>
> >> Client hangs upon copying of large files TO the server. Transfer begins
> >> quickly then hangs, sometimes taking the client o/s with it, until
> >> transfer starts again. In less extreme cases transfer is sporadic.
> >>     I am using nfs4 w gigabit nics.
> >> http://ubuntuforums.org/showthread.php?p=9269703
> >>     It appears that this problem is not restricted to ubuntu and exists
> >
> > Could this perhaps be related to the following bugzilla entry?
> >     https://bugzilla.kernel.org/show_bug.cgi?id=16213
> >
> > If so, then could you please try the proposed fix and see if it helps.
> >
> > Cheers
> >   Trond
>   Thanks Trond,
> The patch solved the client lockups with a patched vanilla kernel (will  
> keep trying with an ubuntu kernel, as it should do the same, but didnt)
> 
> Unfortunatley it dousnt fix the other problem, as it seems they are  
> separate, of the transfer happening in bursts, reducing the actual  
> throughput dramatically. i.e transfer starts at 16mb/s (according to  
> nautilus), then 3 or 4 seconds later the progress bar stops, the hdd  
> activity also stops (its the same with cp of course, nautilus just gives  
> me a good indication of xfer speed), then 4 or 5 seconds later it starts  
> again for 3 or 4 seconds.... repeat ad nausium...
>   Refer to the forum thread for graphs etc. of throughput if nesc.

That is usually because the server is caching too much data instead of
progressively writing it out. When the client calls 'commit' (the NFS
equivalent of fsync()) then the disk on the server goes into a frenzy of
writing, and the client does the RPC equivalent of twiddling its thumbs
until the server is done...

I'd suggest trying to lower the values
of /proc/sys/vm/dirty_expire_centisecs
and /proc/sys/vm/dirty_background_ratio on the server. You might also
try lowering /proc/sys/vm/dirty_writeback_centisecs...

Cheers
  Trond