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Re: [Xen-API] vhdx support ?

Hi Mike,

Thanks for your reply. Well yes vhdx is very new, it is not yet released as it's part of the windows 8 server hyper-v layer which is currently in beta as far as I know. But still this is very interesting and I am a bit worried that windows 8's hyper-v is going to take a big step ahead of other virtualisations solutions. I love Xen and XCP but I must admit that they've implemented really nice features...

I don't think there is any vhdx open source implementation yet. I thought there was a partnership between citrix and microsoft, but maybe I'm wrong.

Still there is the technical specification document available on ms site:


If your storage team want to take a look at it.


On 07.06.2012 10:35, Mike McClurg wrote:
On 01/06/12 23:29, Sébastien Riccio wrote:

I don't know where this question should be posted, but I'll try here.

Is there any plan for XenServer/XCP/Kronos to support the vhdx format
that should get rid of the 2tb limit for a single volume ?

As seen somewhere on the interweb:

Now with VHDX Microsoft kills this limitations and brings some other

  * Supports up to 16TB size
  * Supports larger block file size
  * improved performance
  * improved corruption resistance

I just spoke to our storage team dev lead about this. The short answer is that we want to support it, but we don't have any plans for it in the short term.

The real benefits we would get out of VHDX would be breaking the 2TB limit, and potential performance improvements. Modifying our current VHD implementation might let us do that, without actually implementing VHDX. Perhaps QCOW images might allow disks bigger than 2TB, but I don't really know.

The biggest issue with implementing VHDX is that we don't know of any existing, open-source implementation of it, which means that we would have to invest a lot of time to write our own from scratch. If anyone knows of any existing VHDX implementations that we can use, I'm sure the storage team would like to hear about it!


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