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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.
Peter
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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.
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