New subject: TCP v UDP performance

13 Jun 2002


      *** Before acting on this e-mail or opening any attachment you are advised to read the disclaimer at the end of this e-mail ***
Solaris 6, and we used Sun's own PCI Gigabit 2.0 card (as it's described on
the invoice)
Thanks for the tip though.  I suspect the drivers are probably OK, install
was only done a couple of months back and up to date versions used - unless
you know a previous driver is better.... <g>
Peter
-----Original Message-----
From: Jason S. Cash [mailto:cash@UDel.Edu] 
Sent: 12 June 2002 19:02
To: Peter Bryant
Cc: 'toasters@mathworks.com'
Subject: Re: TCP v UDP performance
On Tue, 11 Jun 2002, Peter Bryant wrote:
...
Sometime ago I posted some performance tweaks for TCP performance, 
which (when the filer was switched to TCP) worked a treat.  I was 
hoping to get the same for UDP.  However...
It seems that UDP on Sun over 1GB Ethernet and above is problematic.  
Some details below (words and details have been changed to protect the 
guilty!). As a result we're sticking to TCP for now.
What version of solaris and what gig-e card?  I would look for a new driver
for the gigaswift adaptor that helps immensly w/ UDP NFS perf.
Jason
...
Peter
=====================================================
I've done a bit of research and found out that testing of a very 
similar setup to yours, by another customer, showed that there is a 
performance bug in the NFS UDP implementation of Solaris.
We all know that NFS over UDP is about 20% faster than NFS over TCP 
however, the Solaris implementation of UDP breaks this rule when 
gigabit Ethernet is involved..!  It seems to be that when NFS is used 
with UDP for internet, 10Mb and 100Mb connectivity then the rule 
applies and also when you have a gigabit Ethernet connection under low 
load then again all is fine.
The performance problem appears when you try to load the gig 
connection heavily - Solaris's UDP simply cannot perform at the 
required rate.  Now, thankfully, the TCP implementation in Solaris is 
very good and is up to the job - hence, the situation you find whereby 
NFS over TCP is much better than NFS over UDP.  This matches exactly 
with your findings where under normal database usage your Gig + 
NFS/UDP connection is fine - but when you try to backup over the Gig 
Ethernet link the load on the network goes up and UDP can't perform.  
You switched from UDP to TCP and the problem went away.
My recommendation to you is to keep using NFS over TCP - the other 
customer has decided to stay with TCP as it works well and they can't 
see any benefit in moving back to UDP.
******************************* Disclaimer

Confidentiality:  This e-mail and any attachments are intended for the
addressee(s) only and may be confidential.  If they have come to you in
error you must take no action based on them, nor must you copy or show
them to anyone; please reply to this e-mail and highlight the error.
Viruses:  Although we have taken steps to ensure that this e-mail and 
attachments are free from any virus, we advise that in keeping with 
good practice the recipient should ensure they are actually virus 
free.
********************** http://www.burallplastec.com ********************
/*  Jason S. Cash  -  Systems Programmer
    IT/Network and Systems Services
    University of Delaware, Newark Delaware
    e:cash@udel.edu  v: 302-831-0461         */

RE: TCP v UDP performance