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

["sven waeyenbergh" <sven.waeyenbergh@xxxxxxxxx>]

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

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