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RE: [Xen-users] Qcow utilities

To: "Fajar A. Nugraha" <fajar@xxxxxxxxx>, Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Qcow utilities
From: Joe Hammerman <jhammerman@xxxxxxxxxxxx>
Date: Thu, 30 Apr 2009 13:34:54 -0700
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Thread-topic: [Xen-users] Qcow utilities
Hi Fajar,
        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'. We 
cannot use NFS booting due to a bug in the kernel version employed by CentOS 
5.3, so that rules out UnionFS and ClusterNFS, etc.
        Qcow images seemed like a pretty good way to satisfy my deliverable - 
can I generate them using another utility?
        Any other advice is appreciated!
        Joseph Hammerman

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Fajar A. Nugraha
Sent: Thursday, April 30, 2009 12:03 AM
To: Xen List
Subject: Re: [Xen-users] Qcow utilities

On Thu, Apr 30, 2009 at 11:18 AM, Joe Hammerman <jhammerman@xxxxxxxxxxxx> wrote:
> Hey all, as a follow up to my earlier communication, it seemed that qcow
> might have the functionality I was looking for. I spent some time trying to
> get it up and going, but wasn't making much progress.

> Given

> https://bugzilla.redhat.com/show_bug.cgi?id=479315

> Does this mean that CoW is broken on CentOS 5.3 with Xen 3.03?

Seems like it.
What are your main goals?
If it's space savings, IMHO usually it's not worthed. For example,
once you do "yum update" on domU and update lots of packages (for
example going from Centos 5.2 -> 5.3), it pretty much destroys
whatever space-saving you may have while still having the performace
penalty of qcow.

This is part of the reason I like zfs volume, either directly on
Opensolaris dom0 or by exporting it (via iscsi) to Linux dom0. zfs
snapshot-clone feature is very efficient, and even in the event of
domU's data change a lot (like the above scenario) you can still have
space savings by turning on compression and setting refreservation=0.



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