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RE: [Xen-users] copy the running image, not working

To: "Xin Chen" <xcheney@xxxxxxxxxxxxxx>, "xen-users" <Xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] copy the running image, not working
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Thu, 31 May 2007 14:11:50 +0200
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Thread-topic: [Xen-users] copy the running image, not working

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Xin Chen
> Sent: 31 May 2007 13:01
> To: xen-users
> Subject: [Xen-users] copy the running image, not working
> Hi All,
> Domain 0 System: Fedora 6,  fc6xen. kernel 2.6.18, because 
> 2.6.20 seems 
> not good.
> Guest system: Fedora 6 and Window 2000 server.
> I was trying to backup the guest system I created.
> The guest system is running(windows 2000 server, 
> full-virtual). I copy 
> the image like: cp win2k win2k.bak
> When it is copied, I change win2k.bak to win2k, and try to start the 
> system using this file, and it stops when starting the windows system.
> Does that mean we can't copy the image when the system is running, it 
> seems the system will write the image file every minuters.

Yes, there's no guarantee that the filesystem on the disk-image is
"correct" at any time except when you've told the OS "you need to save
everything to disk now" - which is usually what happens during a
"poweroff" or "shutdown" situation, and at no other times. 

There are filesystems that are more resiliant than others, but assuming
that you don't actually want to change the filesystem (which is
unlikely, as Windows don't offer much in the way of choice here), you'll
have to make sure you either shut down the server, or use the method
described below. 
> In this case, what 's the best way to backup the guest 
> images. We don't 
> want to shut down the server everytime when we do the backup, right?

The most user friendly way to back things up, in my opinion, is to take
a snapshot of the guest as it runs and the disk-image with it. So you do
something like:

# xm save dom-win2k somefile
# cp winsk.img win2k.img.bak
# cp somefile somefile.bak
# xm restore somefile

This will "shut down" the guest for a few seconds (as long as it takes
to copy the domain content and the files).

You need to save these files together, as the "savefile.bak" will
contain a backup of the unsaved disk-content, and since you're not
actually using the "shutdown" of the domain itself, you'll need that to
recover the disk content later on. 

Note that the save/restore feature of HVM (fully virtualized) domains is
new to Xen version 3.1, so you will have to update your hypervisor and
tools before you can use this feature. 

> Anyone please give me some ideas??
> Thanks a lot!
> x
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