VHD support in Windows? Vista has it already…

Long Zheng has uncovered an interesting job posting at Microsoft, seeking engineers to  "bring virtualization into the mainstream." It’s one of the few (no doubt inadvertent) leaks in the Windows 7 feature set we’ve yet seen:

In Windows 7, our team will be responsible for creating, mounting, performing I/O on, and dismounting VHDs (virtual hard disks) natively.


Virtualization technology has been a great success with Virtual Server and Hyper-V. With native OS support on the horizon it will become an even greater hit. Our team is making this a reality in Windows 7. Consider the simplicity of backup using a VHD, or the portability of a virtual disk backed by a single file. These are a few reasons why this technology is poised to be one of the greatest features in Windows 7–come help us achieve this goal.

In an update, Long notes that a few people he’s talked to have "expressed their concern this may not make it to RTM."

Maybe, but it’s worth noting that support for the VHD format is in Windows Vista today, in the form of the Complete PC Backup program found in the Business, Ultimate, and Enterprise editions. (Here’s an August 2006 demo of the feature, which also mentions the capability of mounting saved VHD files.) So the operating system already has code to create and perform I/O on VHD files.

During the beta for Vista, I recall product managers talking about how they wanted to include a tool to mount and unmount those backup images but ran out of time. That was in summer 2006, around the time RC1 was declared, and presumably the teams responsible for that code continued working on it. No doubt much of the work that has gone into Hyper-V (RC1 just shipped) and Virtual PC 2007 (Service Pack 1 just shipped) could also make it into Windows 7.

Given that base, it’s a safe bet that development of this feature is pretty far along. Far enough, in fact, that whoever wrote that job posting has enough confidence to predict that "this technology is poised to be one of the greatest features in Windows 7." It might have a better chance of making it into the final release than those skeptics think .

Update: In the comments, Greg Duncan points out that Vista users can install the VHDMount utility from Virtual Server 2005 R2 SP1 and use it to mount/unmount VHD files, although it’s not easy. More details in his post here.

From the sidebar at Greg’s blog, I see that he has been living up to his blog’s name by working on some cool-looking Windows LIve Writer templates as well. Nice!

3 thoughts on “VHD support in Windows? Vista has it already…

  1. I so hope this makes it, a lot of persons requested it during the Longhorn client beta. So it is most likely. The feature it guarantees is the ability to boot your installation of Windows 7 on any computer (possibly only Windows 7 PCs) I assume, but then again the ability to have access to your “computer”, all your files, all your applications and settings would definitely be cool. By the time Windows 7 hits market (around 2010 I bet), most external drives will be 2 to 3 TBs standard. I think the ability to mount that same VHD on any computer running Windows 7 would make me upgrade to this release on all my computers in a heart beat. What bothers me though is licensing, would Microsoft allow us to have an additional bootable copy of Windows in the .VHD format, since you could have your external drive while at the same time being able to boot it on another computer while still using the same computer from which it was backed up. Unless there is some validation to prevent you from running multiple copies of the system/license at the same time.

  2. Just FYI… You can download VHDMount and use it today to mount VHD’s as drives.

    With a tiny bit of effort you can also right-click mount/unmount enable them too. 🙂

    The sad thing is that it’s not super easy. That’s why I got a little excited when I read the blurb about the possible native VHD support in Windows 7. To have it baked into the OS would be very cool. On a related note, I really hope additional virtualization tech makes it into W7 and not just drive virtualization. (i.e. having SoftGrid baked in would rock).

    Anyway, how to get and use VHDMount has been covered by many, but I’ve also documented my fun with it on Vista here, http://coolthingoftheday.blogspot.com/2008/01/tell-me-vhdmount-story-installing-just.html

    Hope this helps,

  3. Interesting that when I read about the VHD support in 7 I didn’t make the connection. I have had real time experience with doing a full restore after a reformat reinstall with Home premium. I found that once I pointed the backup in the right direction it worked fantastic, it now qualifies as a “killer app” in my book, right along with search which is hard to without. The full backup in Ultimate is for my needs, is the “Ultimate Extra” and will be why I eventually upgrade all machines to it.

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