Category: SAN

A while ago Cisco added dynamic FCoE support to Nexus 5000 switches. It sounded interesting and I wanted to talk about it in my Data Center Fabrics update session, but I couldn’t find any documentation at that time.

In the meantime, the Configuring Dynamic FCoE Using FabricPath configuration guide appeared on Cisco’s web site and J Metz wrote a lengthly blog post explaining how it all works, triggering a severe attack of déjà vu.

One of my regular readers sent me a long list of FCoE-related questions:

I wanted to get your thoughts around another topic – iSCSI vs. FCoE? Are there merits and business cases to moving to FCoE? Does FCoE deliver better performance in the end? Does FCoE make things easier or more complex?

He also made a very relevant remark: “Vendors that can support FCoE promote this over iSCSI; those that don’t have an FCoE solution say they aren’t seeing any growth in this area to warrant developing a solution”.

A while ago I wrote about ATAoE and why I think a layer-2-only TFTP-like protocol shouldn’t be used these days. As always, the answer to that black-and-white opinion (and I’m full of them) is “it depends” – ATAoE works great if you do it right.

Nicolas Vermandé sent me a really interesting question: “I've been looking for answers to a simple question that even different people at Cisco don't seem to agree on: Is it a good idea to class IP traffic (iSCSI or NFS over TCP) in pause no-drop class? What is the impact of having both pauses and TCP sliding windows at the same time?”

With all the Puppet buzz I’m hearing and claims that “compute and storage orchestration problems have been solved” I wanted to check the reality of those claims – is it (for example) possible to create a LUN on a storage array using a standard well-defined API.

Stephen Foskett, Simon Gordon and Scott Lowe quickly pointed me in the right direction: SMI-S. Thank you!

Chris Marget recently asked a really interesting question:

I’ve encountered an environment where the iSCSI networks are built just like FC networks: Multipathing software in use on servers and storage, switches dedicated to “SAN A” and “SAN B” VLANs, and full isolation of paths (redundant paths) between server and storage. I understand creating a dedicated iSCSI VLAN, but why would you need two? Isn’t the whole thing running on top of TCP? Am I missing something?

Well, it actually makes sense in some mission-critical environments.

Should you use FC, FCoE or iSCSI when deploying new gear in your existing data center? What about Greenfield deployments? What are the decision criteria? Should you just skip iSCSI and use NFS if you’re focusing on server virtualization with VMware? Does it still make sense to build separate iSCSI network? Are jumbo frames useful? We’ll try to answer all these questions and a few more in the first Data Center Virtual Symposium sponsored by Cisco Systems.

A comment left on my dense-mode FCoE post is a perfect example of the dangers of using vague, marketing-driven and ill-defined word like “switching”. The author wrote: “FC-SW is by no means routing… Fibre Channel is switching.” As I explained in one of my previous posts, switching can mean anything, from circuit-based activities to bridging, routing and even load balancing (I am positive some vendors claim their load balancers application delivery controllers are L4-L7 switches), so let’s see whether Fibre Channel “switching” is closer to bridging or routing.

J Michel Metz brought out an interesting aspect of the dense/sparse mode FCoE design dilemma in a comment to my FCoE over Trill ... this time from Juniper post: FC-focused troubleshooting. I have to mention that he happens to be working for a company that has the only dense-mode FCoE solution, but the comment does stand on its own.

Before reading this post you might want to read the definition of dense- and sparse-mode FCoE and a few more technical details.

A tweet from J Michel Metz has alerted me to a “Why TRILL won't work for data center network architecture” article by Anjan Venkatramani, Juniper’s VP of Product Management. Most of the long article could be condensed in two short sentences my readers are very familiar about: Bridging does not scale and TRILL does not solve the traffic trombone issues (hidden implication: QFabric will solve all your problems)... but the author couldn’t resist throwing “FCoE over TRILL” bone into the mix.