2008-09-24 23:05:13

by Bruce Fields

[permalink] [raw]
Subject: Re: [NFS] sync, async, write speeds.

On Wed, Sep 17, 2008 at 09:35:15AM +0200, Chris Fanning wrote:
> Hello all,
> I'm using NFS to mount /home on a gigabit network.
> /etc/exports on the server
> /home,no_root_squash,sync,no_subtree_check)
> /proc/mount on the client
> home_server:/home /home nfs
> rw,vers=3,rsize=32768,wsize=32768,hard,nointr,proto=tcp,timeo=600,retrans=2,sec=sys,addr=
> 0 0
> Write performance is not good.
> dd if=/dev/zero of=/home/testfile bs=16k count=16384
> 268435456 bytes (268 MB) copied, 45.0461 seconds, 6.0 MB/s
> If I change the export to async, it improves a lot.
> dd if=/dev/zero of=./testfile bs=16k count=16384
> 268435456 bytes (268 MB) copied, 3.6 seconds, 74.4 MB/s
> But the recommendation is not to use async, right?
> I've tried the same thing on two different servers (one xenified
> kernel, one stock etch kernel) and two different clients (ubuntu 7.10
> y debian etch), with the same results. :(
> Where should I start looking to fix this?

What's the maximum sustained bandwidth to the server's disk? With
enough server memory, a 268MB write could just be going straight to
memory in the async case.


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