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[Xen-devel] Re: [Xen-users] Xen 4.1 Feature Request List

On Wed, Apr 07, 2010 at 01:59:40PM -0700, Grant McWilliams wrote:
>    On Wed, Apr 7, 2010 at 7:51 AM, Pasi KÀrkkÀinen <[1]pasik@xxxxxx> wrote:
>      On Wed, Apr 07, 2010 at 04:13:07AM -0700, Grant McWilliams wrote:
>      >
>      > Â  Â These might not be wishes for 4.1 as some may be too big but
>      they're my
>      > Â  Â wishlist anyway. Note they also might not be things that belong
>      to the
>      > Â  Â Hypervisor but rather to tools associated with.
>      >
>      > Â  Â  1. Make qcow2 actually work and include backing files.
>      >
>      Have you checked out blktap2 VHD support? Does it work for you?
>    I haven't. I thought it was only commercial Xenserver that supported VHD.

Xen 4.0.0 includes blktap2 support in the tools: 

You also need a kernel with the blktap2 driver:

(that XenKernelFeatures wiki page is still a work-in-progress and might not be 
complete yet).

>      See: [2]http://wiki.xensource.com/xenwiki/XenCommonProblems
>      for links.
>      > Â  Â  Â  Â  Â 1. If it can't be made to work then it should be taken
>      out and not
>      > Â  Â  Â  Â  Â  Â  mentioned in the docs so we don't waste weeks trying
>      to get it to
>      > Â  Â  Â  Â  Â  Â  work.
>      >
>      From which docs?
>    The internet! :-) I assumed that qcow was in the docs since Xen supports
>    it and it's mentioned all over the forums. It very well might not be
>    mentioned in the docs but it has some support for qcow that no matter
>    which version of xen or Centos I used I ran into some bug that stopped me
>    from using it. As class as I got was to use qcow images as disks but with
>    no backing store which I don't think makes a whole lot of sense.

I guess blktap2/vhd was developed because of qcow wasn't that good.
>      > Â  Â  2. Figure out why you can't start a VM with a disk image
>      residing in a
>      > Â  Â  Â  Â ramdisk (bug?)
>      I have never tried this one. Which disk backend did you use?
>    I was using tap:aio disk images with Xen 3.4. I really wanted to use a
>    qcow2 backing disk in a ram disk so all reads would be super fast then the
>    writes would go to the RAID. I then stepped down from that lofty goal and
>    tried to get any DomU to boot from any image in ramdisk and it would error
>    immediately. It's been a while now so I don't remember the error. I could
>    try it again though.


-- Pasi

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