Xen project Mailing List

On Jan 4, 2008 11:47 AM, chetan saundankar <chetan.lists@xxxxxxxxx> wrote:

Hi Sven,
Thanks a lot for replying. Yes I am looking for the solution that you
have described in your mail.
Now I would like to know couple of things regarding COW,

1. Is there any requirement of installing any package or updating
configurations within the guest VM? if yes is there any work around.

Yes, you will have to install COW-capable drivers on domU. There are several different possibilities, they are listed on the link in my previous mail. I think the best option is o use this one : http://wiki.xensource.com/xenwiki/InstructionsFromMichaelLang
That one uses unionFS. I think that is available from the standard redhat distribution.

2. How to deploy Fully Virtualized guests in the COW fashion?

i doubt very much that this is possible on HVM domains. The question if this is possible or not is actually more dependant on the distribution that you will use on domU than on xen itself. If you choose a distribution that can be installed on a COW filesystem, it should also be possible in xen. I personally think a redhat system is the best choise, ince there are a lot of readme's for redhat out there.

Regards

Chetan

On Jan 4, 2008 3:50 PM, sven waeyenbergh <sven.waeyenbergh@xxxxxxxxx> wrote:
> It sounds like you need a COW filesystem.
> COW stands for copy on write. This means that you have a single root
> filesystem that is shared by all guests, and each guest has an extra volume
> that he will use to write any changes to (instead of the root filesystem).
> it's a bit like a snapshot works.
> This enables you to have a single image for multiple machines, and you can
> even have local changes for each machine.
> Note that this will be a very bad idea if performance is important to you.
>
> I'm sure this worked with xen2.0, i'm not sure of the support on xen
> 3.0/3.1, but you should be able to find more info here:
> http://wiki.xensource.com/xenwiki/COWHowTo
>
> S
>
>
>
> On Jan 3, 2008 11:35 PM, chetan saundankar <chetan.lists@xxxxxxxxx> wrote:
> >
> >
> >
> > Hi all,
> > I am having following deployment scenario,
> > - 2 Xen hosts (running Xen 3.1)
> > - 1 Image server (NFS)
> >
> > Requirements:
> > -----------------
> > 1. Have an file system image of a linux distribution say Fedora 8 on
> > Image (NFS) Server
> > 2. I want to have 4 guests running Fedora 8 but for 4 different users.
> > 3. Base file system image (Fedora 8 image on Image server) shared
> > amongst 4 users in Read only fashion
> > 4. All 4 users will have separate VBD's for user specific data.
> >
> > Question:
> > ------------
> > Is there any way to force users write on the data VBD's exported for
> > each VM?
> > The whole point is that guest user should not worry about where to
> > write, every write call should be targeted towards data VBD and this
> > needs to be achieved without changing anything in the guest.
> >
> > Thanks and Regards
> > Chetan
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
> >
>
>

Re: [Xen-users] Shared storage in Xen Cluster