When spec'ing and configuring a machine that will utilise shared iSCSI storage, I've read a lot of documentation which suggests a dedicated network adapter should be used for iSCSI communication. That makes a lot of sense and I have no problem with it. The question I do have, is this - should that suggestion be taken to mean that a separate physical NIC should be used, or will a dedicated port/ports on a dual/quad port NIC be just as good? My suspicion is that simply using dedicated port(s) on a shared NIC would be just as good.
Any input greatly appreciated.
PCI-x/PCI-e bus-speeds are such that unless you're talking 10GbE, dedicating one port on a quad-port NIC is all you really need. The card will have enough bandwidth to handle full-streaming on all ports (whether or not the server it's in can handle that is another story).
Where a dedicated NIC comes in handy is if that NIC can perform as an iSCSI initiator from firmware. This turns the NIC into a dedicated storage adapter, which can be more reliable than a pure software iSCSI stack.