RE: [Xen-Users] How to clone a VM when it is running?

[Robert Wicks <rwicks@xxxxxxxxxxx>]

I use Citrix Xenserver, and the VMs hard drives are LVM logical volumes, not 
images sitting on a filesystem. I was not aware copy could do sparse files, 
though, so thanks for the tip!
--
Robert A. Wicks
Systems Engineer
desk: (404) 888-2428
mobile: (404) 606-4622
rwicks@xxxxxxxxxxx
________________________________________
From: Brian Krusic [brian@xxxxxxxxxx]
Sent: Friday, March 20, 2009 5:22 PM
To: Robert Wicks
Cc: Xen-Users
Subject: Re: [Xen-Users] How to clone a VM when it is running?

Hi Robert,

Why do a dd when you can just cp or even cp --sparse=always?

Why restore to en empty VM when you can just use the copied image on a 
different box?

Just tryin to see of I can adopt some techniques.

- Brian




On Mar 20, 2009, at 10:35 AM, Robert Wicks wrote:

FWIW, I have taken an LVM snapshot of a running Windows VM, done a dd out to a 
file on an NFS mount point of the snapshot, and restored the resulting file 
inside an empty, but identically sized VM on another Xenserver host without any 
issues. The Windows box basically reacts like you just cut power.  A checkdisk 
is the worst which has happened, and I always have something I can use in the 
output file. I wish there were a way to generate an XVA file from this output 
so that I could just import the snapshotted backup as a normal Xen image.

Robert A. Wicks
ITC Engineer
desk: (404) 888-2428
mobile: (404) 606-4622
rwicks@xxxxxxxxxxx<mailto:rwicks@xxxxxxxxxxx>

From: 
xen-users-bounces@xxxxxxxxxxxxxxxxxxx<mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx>
 [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Brian Krusic
Sent: Friday, March 20, 2009 12:40 PM
To: Nick Couchman
Cc: freddie weng; Xen-Users
Subject: Re: [Xen-Users] How to clone a VM when it is running?

Hi Nick,

I've experimented using LVMs and creating a snapshot volume of the root 
partition where my vms live (/var/lib/xen/images).

You can then do whatever want with what's on the snapshot volume.  So for 
example. your virtual machine image is in a state in time when the snapshot was 
taken.

Keep in mind that when you create a snapshot of VMware instances, it pauses the 
VM before doing its thing.

When running popular cloning sw like Norton Ghost, etc... the machines state is 
also fixed in time so I think you won't really be able to get around the 
state-in-time/cloning thing.

- Brian




On Mar 20, 2009, at 8:35 AM, Nick Couchman wrote:


Cloning a VM while it is running isn't really a great idea.  In order to 
maintain filesystem consistency, at the time of the clone all filesystem 
activity must be frozen and data needs to be flushed from the caches and 
buffers out to disk devices.  If order to do this while the VM is running, you 
have to interact with the O/S of the VM to freeze filesystem transactions (XFS 
is the only filesystem I've used that supports this), flush out the buffers and 
caches ("sync"), then clone the disk image, then unfreeze the filesystem.  A 
much easier option is to pause the domU temporarily ("xm pause <domU>"), clone 
it, then unpause.

Why is being able to clone while a domU is running so critical to you?

>>> On 3/20/2009 at  9:26 AM, freddie weng 
>>> <freddieweng@xxxxxxxx<mailto:freddieweng@xxxxxxxx>> wrote:
Hi everybody,

I found that we can use virt-clone to clone a VM but only when that VM is not 
running.
This is not useful most of the time.
Can we clone a VM even when it is running?

It's critical to my research, any idea is much appreciated!!!!


all the best,
Freddie


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