Alexandre Lecuyer wrote:
> Hi list,
>
> We've had an interesting NFS performance issue with the following setup.
> Clients : CentOS 5.5, kernel 2.6.18-194.el5
> Server : Solaris 10 kernel Generic_142901-08
>
> Reading a file (not cached) with dd : dd if=file1 of=/dev/null
> bs=1024k count=100
> performance is around.. 700 kB/s !
>
> /proc/mounts shows rsize has been negotiated to 1mB
>
> If we force rsize to a smaller value, 32kB, the problem goes away and
> we're back around 70/80 mB/s read performance.
>
> Wiresharks show something interesting in the first (slow) case:
> It seems that the NFS client is "waiting" between requests:
>
>
> 1473 11.756852 client.net nfs1.net TCP 868 > nfs [ACK] Seq=9345
> 1474 11.757888 nfs1.net client.net RPC Continuation
> 1475 11.797837 client.net nfs1.net TCP 868 > nfs [ACK] Seq=9345
> 1476 11.798877 nfs1.net client.net RPC Continuation
> [....]
>
> Notice how the server replies within about 0,001s, but the client
> appears to be waiting 0,04s before asking for the next bit.
> (we captured the traffic from the client). This pattern repeats for
> the whole exchange
>
> It's likely we missed something, can't figure it out.. has anyone seen
> this before ?
>
> Cheers,
>
> Alex
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Well, it's been a long time since I've done troubleshooting on large NFS
networks, but here's an idea...
Are you seeing any kind of packet loss/retransmissions? Take a look at
netstat -s. When I last did this work it was with NFS over udp, but I
think retransmitted packets will cause more performance loss with large
packet sizes. I used to find machines with broken ethernet interfaces
that would cause these kinds of problems.
Nataraj
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