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10/16/2008
09:29 PM
Charles Babcock
Charles Babcock
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Crosby: Walk The Walk, Yes, But Not Down The OVF Path

In the wee hours of the morning recently, I posted a blog addressed to the virtualization vendors: "It's Time To Walk The Walk, Not Just Talk," advocating greater use of the recently emerged OVF standard. Simon Crosby, CTO of Citrix Systems' XenSource unit, was four time zones away in Cambridge, England, but it only took him about four hours to track me down.

In the wee hours of the morning recently, I posted a blog addressed to the virtualization vendors: "It's Time To Walk The Walk, Not Just Talk," advocating greater use of the recently emerged OVF standard. Simon Crosby, CTO of Citrix Systems' XenSource unit, was four time zones away in Cambridge, England, but it only took him about four hours to track me down.It didn't take him long to enlighten me. Citrix is a supporter of OVF and an originator of tools that implement OVF, the open source Kensho Project. I knew Citrix was a Kensho sponsor. I wrote about the pending tools July 16. As far as I knew, I was about the only one, with the exception of a blogger named Billy Marshall, who did write about them. I still wanted to say it was about time the virtualization vendors moved OVF to center stage.

And therein lies the rub. Crosby pointed out convincingly that it's not a matter of issuing the next version of XenServer with support for Open Virtual Machine format and sending its favored VHD format back to the minor leagues. They are two different things. VHD and VMware's VMDK are runtime formats for executables, pulling the virtualized files off disk in a way that a hypervisor can understand how to execute them.

OVF, on the other hand, is an export or migration format, a way of structuring the virtual machine files so they contain the right information in the right sequence so they can be moved out from under ESX Server and be recognized by Hyper-V or XenServer, or vice versa. The format contains metadata that tells hypervisor the things it needs to know about how to seize and construct the files handed to it.

His conclusion was: So you can't move a little-known, understudy format into the limelight and claim it's ready to displace the established stars. It's there for migration purposes, nothing more. That's what I like about Simon Crosby: a deep technology understanding, often accompanied by the unvarnished truth.

I said in my blog that VMware pioneered OVF as a neutral format to thwart a de facto standard from emerging, since Microsoft and Citrix had united on VHD. VMware itself says it "pioneered" OVF in some of the materials on its Web site. The part about wanting to forestall a de facto standard was my speculation on why VMware decide to back a neutral standard when it did.

But Crosby enlightened me some more. "We'd done a ton of modeling on a portable format," he said. "Dare I say it? We came up with it." Dell liked the model, but Dell advocated that VMware and others should be in on it. "I'm not sure XenSource would have talked to VMware by itself, but Dell insisted," Crosby related. VMware had ideas about how to fit a portability format into a virtual infrastructure, Crosby concedes. IBM, HP, and lastly Microsoft, by his account, joined in. XenSource needed OVF because VMware is the market leader, and it's in XenSource's interest to have a way of getting the market leader's virtual machines away from ESX Server and over to XenServer (or, for that matter, Hyper-V).

Ah, I have to agree that's a pretty good reason for XenSource to want an OVF format.

I received comments from many readers on this blog, one of them coming from what sounded like a well-informed VMware employee, also with a deep technical understanding. "Charles, I can understand the confusion with OVF. Let me highlight a few things," he began, sounding a lot like Crosby.

"First, OVF was in a draft form up until just recently. It's hard for any one vendor to write their product to a draft since things change between the draft and the release," he wrote. VMware has supported OVF in its Workstation and Converter products for the past eight months. "Nearly all of the VMs on the VMware Virtual Appliance Marketplace are in OVF format now. I say supporting, as in importing, just like you highlighted in the article."

Crosby referred to OVF as an export format; the presumed VMware employee referred to it as an "import" format. I guess the nomenclature depends on whether you're the dominant vendor or not.

Which brings me back to my original Time To Walk The Walk point. If we now have a neutral export/import format, why can't we have a neutral runtime format that everyone could adhere to, saving virtualization customers tons of headaches? OVF isn't it, I now understand. But what will be?

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