[CentOS] ext3 heavy file fragmentation with NFS write

[Stephen John Smoogen]

On Fri, Feb 27, 2009 at 12:31 AM, Andrzej Szymański <szymans at agh.edu.pl> wrote:
> Hello,
>
> Does anybody know how to avoid the file fragmentation when a file is
> created over NFSv3?
>
> A file created locally is OK:
> dd bs=32k if=/dev/zero of=test count=32x1024 conv=fsync
> filefrag test
> test: 10 extents found, perfection would be 9 extents
>
> When I create the file in the same dir, but from another machine,
> mounted over NFS:
>
> filefrag test
> test: 4833 extents found, perfection would be 9 extents

1) what is filefrag and where is it from?
2) Have you played with adding/subtracting threads to see if that helps?
3) What happens if you don't use fsync on the dd.
4) What happens if you use larger/smaller bs
5) Is the rsize/wsize onthe server 32768 or some other number. I
thought the default w/size on an export was 512 or some small number.

> With such a file a sequential read is quite slow (~76MB vs >200MB on my
> raid card).
>
> I can just suspect that this is a problem of block allocation when the
> same file is appended by different processes (8 NFS threads).
>
> I've tried mounting ext3 with -o reservation and switch to NFS over TCP,
> with no improvement.
>
> Both systems are Centos 5.2 with kernel 2.6.18-92.1.22.el5
> The ext3 is mounted with rw,nosuid,nodev,usrquota,grpquota,acl
> NFS export: rw,sync,no_root_squash
> 8 NFS threads.
> Remotely mounted with options
> rw,intr,nfsvers=3,proto=udp,rsize=32768,wsize=32768
>
> I would be very grateful for any help.
>
> Andrzej
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>



-- 
Stephen J Smoogen. -- BSD/GNU/Linux
How far that little candle throws his beams! So shines a good deed
in a naughty world. = Shakespeare. "The Merchant of Venice"