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Re: [Xen-API] vhdx support ?

I also googled around and found out that something was cooking at qemu to support vhdx files:


  • VHDX (MS Hyper-V) image format has initial read-only support. Dynamic and fixed sized disks are supported, but not differencing images (e.g. VHDX images with a backing file). Read-only is strictly enforced, and the 'readonly=on' option must be used for any VHDX images.


Maybe I'm wrong but it seems that upstream qemu will be used in a not so far distant future to support Ceph filesystem aswell


Maybe a dream come true ? :)


On 11.07.2013 05:57, srinivas jonn wrote:

this is an existing  VHDX implementation (opensource) for XenServer storage team to consider:


"DiscUtils is a .NET library to read and write ISO files and Virtual Machine disk files (VHD, VDI, XVA, VMDK, etc). DiscUtils is developed in C# with no native code (or P/Invoke)"

From: Sébastien Riccio <sr@xxxxxxxxxxxxxxx>
To: Mike McClurg <mike.mcclurg@xxxxxxxxxx>
Cc: "xen-api@xxxxxxxxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxxxxxxxx>
Sent: Monday, 11 June 2012 3:10 PM
Subject: 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

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:
>> Hi,
>> 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
>> improvements:
>>  * 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!
> Mike

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