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Monday, August 27, 2012

FCoE vs FC (vs iSCSI)

In contract to the legacy setup, the seperate fibre channel and ethernet switches will be replaced by Cisco Nexus 5000 series and the servers will be equiped with network adapter that simulate Eth and FC in one.

A quick high-level overview:

What is FCoE exactly?
FCoE transports Fibre Channel over Ethernet. It does this by replacing the FC0 and FC1 layers of the Fibre Channel stack with Ethernet headers. And since FCoE doesn't change anything to the FC transmissions, it can integration perfectly into the existing Fibre Channel networks.
So basically, SAN's can be cabled with ethernet instead of Fibre Channel, reducing complexity.

NO! iSCSI runs on TCP and IP. FCoE runs directly above Ehternet in the Network layer of OSI. What does this mean? Basically it means that FCoE is not routable and therefore will not work across router IP networks.

Why FCoE?
FCoE will only be used in data centers (I guess) as an alternative cabling for the SAN environment. And it has some very clear benefits over FC:
1. reduces cabling significantly
2. it can handle very high physical I/O connections
3. a single network switch suffices
4. fewer NIC's in the servers
5. fewer hardware means power and cooling costs are reduced

Here, a big TCO calculation has preceded the project that is starting now, in which it was clear that since hardware was needing to get replaced, FCoE was the way to go.

Perhaps something to look into yourself when you are thinking of replacing old hardware?

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