If you read the release notes, Chelsio and Netxen are iffy choices for 10gbe NICs. I'm using intel based 2-port 10gig cards and they work great. I had major problems with NetXen cards which I was using before these.
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Intel on the DSS side, Chelsio on the VM side. (They were NetXen)
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Are you using Block I/O or File I/O for your Volumes? Either way, check the following and retest:
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File I/O
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From the Console: Ctrl + Alt + W -> Enter Admin Password -> Tuning Options -> iSCSI Daemon Options -> Target Options -> Pick your target
MaxRecvDataSegmentLength: 8192
MaxBurstLength 262144
MaxXmitDataSegmentLength: 8192
FirstBurstLength: 65536
DataDigest: None
MaxOutstandingR2T: 1
InitialR2T: Yes
ImmediateData: No
HeaderDigest: None
Wthreads: 8
Have you tried to enable jumbo frames on the switch / DSS / ESX? I found this article relating to this :
http://www.interworks.com/blogs/kcul...s-vmware-esx-4
I am not using Jumbo Frames, however you can try it...