Latency. difference between iSCSI and FCoE
It's been a while since I worked on this stuff, but if I remember correctly the reason for the improved latency is that iSCSI utilises the TCP/IP stack which is built to handle a lossy link, whilst FCoE assumes a pretty much perfect link, communicating directly with the ethernet layer and relying on ECC to handle any rare errors passed up from the ethernet layer.
Basically iSCSI shoehorns standard SCSI commands over an the standard TCP/IP protocol, whereas FCoE just swaps out the standard FC OSI layers 1/2 for ethernet, but uses the FC protocol stack to handle all the layers above that.
Or something like that!
Biting the hand that feeds IT
