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RE: [Xen-users] Qcow utilities

Granted. They actually said they want the machines to essentially have a shared 
filesystem, but write the differences between them to disk. The objective is 
not to save space but because they believe it will keep the machines more 'in 
sync' (not true, as you pointed out).

Is there any way to build Xen with a shared filesystem if CONFIG_NFS_ROOT 
cannot be enabled? There is a bug in the kernel version of CentOS 5.3, and the 
only work around is to compile in the functionality statically, which 
management has ruled out.

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Simon Hobson
Sent: Thursday, April 30, 2009 1:55 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Qcow utilities

Joe Hammerman wrote:

>         The main goal is a to use a shared root image for a set of
>Virtual Machines. Management thinks this will keep the machine more
>'in sync'.

It won't, not unless you use it AS A SHARED FILESYSTEM

If you use any form of COW image then each guest will diverge -
update a file on each guest and each guest will have a separate copy
of the file. You CANNOT update the base image as that would
immediately corrupt ALL the images that rely on it.

If you use a shared filesystem then you could stop the guests, update
the shared filesystem, and restart the guests - though you may
actually get away with guests running depending on what you are

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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