What Does FCoE Have To Do With VM Mobility?

I recently read over Stephen Foskett’s Eight Unresolved Questions About FCoE article, in which he outlines eight topics that should be addressed/prioritized in order to make FCoE, in his words, “truly world-class”.

One of these topics was virtual machine mobility. Here’s what Stephen wrote under the heading “How Do You Handle Virtual Machine Mobility?”:

As I described recently, virtual machine mobility is a major technical challenge for existing networks. The VMware proposal, the VXLAN, seems to be gaining traction right now. But this is only a solution for data networking. How will FCoE SANs handle virtual machine mobility? This remains unresolved as far as I can tell, though Ethernet switch vendors have come up with their own answers. Brocade demonstrated just such a solution at Networking Field Day 2, and I know that others have answers as well. But will there be an interoperable industry solution?

My response to Stephen’s question is pretty simple: VM mobility isn’t a problem for FCoE. VM mobility is a problem for all storage, regardless of protocol.

In my view, tying VM mobility to FCoE is simply buzzword hype. Let’s look at this from a technical perspective—what is so different about FCoE compared to FC, iSCSI, or NFS with regard to VM mobility? Nothing! Regardless of storage protocol, when you move a VM from one data center to another data center, the VM’s storage is still going to sit back in the original data center. The protocol whereby we access that data doesn’t change that fact.

Yes, you can route the IP-based protocols (iSCSI and NFS), which might give you some additional flexibility. But the migrated VM’s storage is still going to sit in the original data center—the only thing you’ve accomplished is introduced some additional latency by adding routers into the mix.

As you can see, VM mobility and storage isn’t an FCoE problem—it’s a storage problem, plain and simple. Protocols can’t fix it. What’s needed to fix it is a fundamental shift in how storage is designed. We need distributed file systems (not just clustered file systems), distributed caching algorithms, greater integration between the block storage and the distributed file systems, greater hypervisor awareness of the underlying storage topology, and more efficient data movement mechanisms. Until then, we can rage all we want about how this protocol or that protocol doesn’t address VM mobility, but we’re simply missing the mark.

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  1. Scott DeShong’s avatar

    I couldn’t agree more. The question I have is if the current storage protocols and standards are capable of being altered to support VM mobility. Should we rely on external storage system applications instead of protocols? And the biggest question in my mind is how to overcome the latency issues when writing to storage? Synchronous replication over long distances or remote storage access over long distances both provide unacceptable latency.

    At the end of the day I view this more as an upper layer (application) issue than a layer2/3 protocol problem.

  2. Dmitri Kalintsev’s avatar


    What about the storage virtualisation technologies, like VPLEX?


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