OT: Diagnosing NFS Performance Problem with Retransmission Timeouts

From: Ben McCann (bmccann@indusriver.com)
Date: Tue Feb 29 2000 - 07:22:13 EST

Sorry for the off-topic posting, but I have a NFS performance problem that has
me stumped. I have three PC's:

                S
               / \
              / \
             C1 C2

S: Linux 2.2.13 on Pentium 233 MMX (NFS Server)
C1: Linux 2.2.15pre10 on AMD K6-450 (NFS Client)
C2: Linux 2.2.15pre10 on Pentium 200 MMX (NFS Client)

My problem is NFS performance between C1 and S sucks but it works great between
C2 and S. I'm getting _many_ timeouts between C1 and S and none between C2 and
S.
(About 10% of my client RPC calls are timing out according to nfsstat). Note
the timeouts appear to happen most when I transfer large files. I get hardly
any when I do something like 'ls -lR' over a large NFS mounted directory tree.

I thought this could be flaky hardware but TCP performance is fine. For example:

        C1 - S (NFS read) ~200 KBytes/Second
        C2 - S (NFS read) ~1000 KBytes/Second
        C1 - S (FTP get) ~1000 KBytes/Second

All tests are on a 10baseT network connected via a hub.

Any ideas on how I can track down the cause of these timeouts? (The timeouts
are reported via nfsstat). I don't see any other errors reported via 'dmesg'
or via /var/log/messages on either the server or the client.

I thought it _might_ be a Linux bug but the two clients are running the same OS.
(Note, however, they do have different ethernet NIC's. Client C1 has a dumb ISA
NE2000 clone and client C2 has a Tulip PCI ethernet NIC). I also tried running
2.2.13 on client C1 and that didn't change the NFS behavior.

Finally, I toyed with running NFS over TCP but the mounts fail when I select
TCP in fstab. (Client says the connection was refused despite the fact that
rpcinfo -p on the server shows TCP listener's running). I haven't tried to
diagnose that yet...

Thanks for any suggestions,
Ben McCann 

-- 
---
Ben McCann                              Indus River Networks
                                        31 Nagog Park
                                        Acton, MA, 01720
email: bmccann@indusriver.com           web: www.indusriver.com 
phone: (978) 266-8140                   fax: (978) 266-8111

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