Jumbo frames being good or bad, depends heavily on the switching infrastructure. If the switches are not sufficient to handle jumbo frames and flowcontrol, then performance could be worse with Jumbo frames enabled.
If the switches are not on the certified list for EQL arrays, I tend to start with standard frames, get a baseline run, then try Jumbo Frames incrementally and make sure things don't get worse.
Jumbo Frames can provide a benefit, it will never be a huge increase, but it does improve the network efficiency and might reduce CPU overhead. That are not a requirement for EQL iSCSI environments.
Please check out the best practices with ESX document. That can really help maximize your performance with EQL storage.
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