NetApp has written a technical paper “Performance Report: Multiprotocol Performance Test of VMware® ESX 3.5 on NetApp Storage Systems” on performance test using FCP, iSCSI, NFSon on Vmware 3.5. Do read the article for good details. I have listed the summary only.

Fibre Channel Protocol Summary

1. FC achieved up to 9% higher throughput than the other protocols while requiring noticeably lower CPU utilization on the ESX 3.5 host compared to NFS and iSCSI.
2. FC storage infrastructures are generally the most costly of all the protocols to install and maintain. FC infrastructure requires expensive Fibre Channel switches and Fibre Channel cabling in order to be deployed.

iSCSI Protocol Summary

1. Using the VMware iSCSI software initiator, we observed performance was at most 7% lower than FC.
2. Software iSCSI also exhibited the highest maximum ESX 3.5 host CPU utilization of all the protocols tested.
3. iSCSI  is relatively inexpensive to deploy and maintain. as it is  running on a standard TCP/IP network,

NFS Protocol Summary

1. NFS performance was at maximum 9% lower than FC. NFS also exhibited ESX 3.5 host server CPU utilization maximum on average higher than FC but lower than iSCSI.
2. Running on a standard TCP/IP network, NFS does not require the expensive Fibre Channel switches, host bus adapters, and Fibre Channel cabling that FC requires, making NFS a lower cost alternative of the two protocols.
3. NFS provides further storage efficiencies by allowing on-demand resizing of data stores and increasing storage saving efficiencies gained when using deduplication. Both of these advantages provide additional operational savings as a result of this storage simplification.