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 */