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Re: [Xen-API] vhdx support ?

On 11/07/13 05:45, Sébastien RICCIO wrote:
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 ? :)


Getting upstream qemu into XenServer is on the work list for the next three months, so it's possible this will come soon to xapi. VHDX support won't just come free with qemu, though; it'll take a lot of work in the storage managers and supporting infrastructure. I'm really not sure when VHDX support is going to make it onto the roadmap, but I know it's on the storage team's minds.


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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