It looks like we have resolved the issue, and by we, I mean Force10 tech support. To recap, after setting up our new EqualLogic array , connected to two Force10 S4810 switches and an ESXi 5.1 host using an Intel X520 NIC, we were having connection issues. 5-8% retransmits (as measured from SAN HQ), high latency spikes on the ESXi host, The EqualLogic MPIO was not working properly, usually only one connection per volume at a time was working, frequent re-connections to the VMFS volume, pings would drop to the SAN, basically it was unusable. We began by troubleshooting the ESXi host, but that lead nowhere, other than a helpful driver update that allowed me to enable FlowControl on the NIC. Eventually we figured out that if we shut off one of the switches, the problem went away. Then we figured out that if we left both switches up but pulled the plug on one of the Port Channel connections, the problem went away. The F10 S4810 switches are connected to our 1 gig SAN via a 10 GbE port channel, connected to two interfaces, one on each F10 switch. The F10 tech support agent figured out by looking at each stack config that the Cisco 3750Es had a dynamic port-channel config, and the F10s had a static config. So he re-built the port-channel on the F10s and made it dynamic, and for the last couple of hours, it has been working correctly, no re-transmits, no latency spikes, no connection drops. I would have never guessed the port-channel was working right because it never dropped a link. But the Force10 tech was very methodical and eventually figured out the port-channel was to blame. Anyway, I hope that this helps someone out there someday. Definitely a strange problem that required turning on and off  switches and pulling cables to track down.
Hello, Configuration Setting up our first R710 host running ESXi 5.1, with a dual-port Intel X520 10GbE card for sw iSCSI, connected to a PS6110XV through Force10 S4810 switches. DCB is disabled on the PS array. No warnings/errors in the logs. It's running the 5.2.5 firmware. The EQ MEM 1.1.1 is installed with storage heartbeat properly configured on the ESXi host, and appears to be working fine. DelayedAck is disabled, and iSCSI login timeout is set to 60s. The Force10 switches have jumbo frames and flow control rx on tx on setup, and they are stacked. A test virtual machine is setup and running on a test volume. Problem Seeing high latency issues on the host. Using the vSphere Client to watch read/write latency on the sw iSCSI HBA. In the past hour, the max has shot up to 7000 ms, with a couple of other bumps in the 1000-2000 range. In between these peaks is generally seems low, less than 10 ms. During the configuration of the Intel NICs, I noticed I cannot enable flow control. The default setting is autonegotiate on, rx off, tx off. I've tried a couple ways to enable it and even added it to the startup script and it still says it is disabled, when viewed with the ethtool -a vmnicx command. Can someone point me in the right direction on where to look for a problem? This is my first run with 10GbE, our current production setup uses ESX 4.1u2 at 1GbE, and it runs fairly well, certainly no latency above 100ms.
ESXi 5.1, Intel X520, PS6110XV - Latency issue