From: Goetzman, Dan (Dan_Goetzman@bmc.com)
Date: Fri Jan 09 2004 - 09:50:16 EST
Howdy admins,
Problem: Fast NFS server causing SLOW NFS reads on Tru64 clients
Server is a dual ES40 TruCluster 5.1A+PK5, gigabit attached
Clients are any Tru64 client all 100BT. No Tru64 100BT clients seem OK as
far as I can tell.
What I think I know...
Problem is due to server being very fast (ES40 4 CPU and gigabit NIC) and
the client's are being over run (discarded UDP packets). The clients that
seem to be the worse are all Tru64 clients on 100BT NIC. Looks like NFS
retransmissions due to dropped packets on the client side. All the NFS
mounts are via the automounter and Tru64 seems to default to NFSV3, UDP, and
a r/w size of 49152. Looks like Tru64 tries to use UDP NFSV3 and a large r/w
size (offered by the Tru64 based NFS server) to have fast NFS transfer rates
(OK as long as we do not drop packets). The same Tru64 clients to a Linux
NFS server are not a problem, but I see the Linux NFS server only offers a
8192 r/w size.
I have not figured out how to tell the TruCluster server to offer a smaller
r/w size at the NFS mount time. It appears hard coded to 49152. And if I
could, this would slow down ALL the NFS clients.
I tried to set udp_recvspace on the client and udp_sendspace on the server,
but the changes made no difference. The Tru64 tuning guide even states that
NFS UDP is not effected by these setting. So, I could not figure out how to
tune around the problem so far.
I can manually mount with a lower r/w size and all seems well. But, I NEED
to use the automounter and it appears that we cannot change the automounter
default action. I would like to do something like change automounter default
to use TCP (I would get flow control) or maybe set the r/w size down
(apparently automounters defaults are hard code?). I want to tweak just the
Tru64 clients (and maybe a few other old and slow clients) so that the
server can still offer the larger r/w sizes for clients that can handle it
and therefore run at the faster rate.
Anyone have any knowledge on all this and any ideas on how to get the Tru64
clients to work well via automounter?
Dan Goetzman
IS-PM&D Support
BMC Software, Houston Tx.
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