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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.

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It depends a bit on which NIC you're using. Some NICs have iSoE, which may allow using both iSCSI and "normal" traffic over both the same NIC chip and port (with vLAN separation, QoS on the wire, and internal prioritization for the Storage traffic). Other do not offer any acceleration and should generally have separate ports (2 should be your minimum for MPIO), though separate NICs are rarely necessary. –  Chris S Mar 24 '12 at 23:35

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up vote 5 down vote accepted

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.

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