Re: Fwd: [Xen-users] differencing disks

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

On Friday 09 July 2010 10:42:41 Alex Edwards wrote:
> ---------- Forwarded message ----------
> From: Alex Edwards <edwards.alex@xxxxxxxxx>
> Date: Fri, Jul 9, 2010 at 9:40 AM
> Subject: Re: [Xen-users] differencing disks
> To: Bart Coninckx <bart.coninckx@xxxxxxxxxx>
> 
> 
> yes I do believe that it is snapshoting, Differencing disks appears to be a
> msoft term given to their VHD tech. I could use snapshots but its more than
> I need. I want 1 point that i always go back to. Could I create a system
> image that can just be remounted when I want to go back? If i had an image
> of my system at a point in time, how fast could I remount it in a different
> VM?
> 
> thanks
> Alex
> 
> On Fri, Jul 9, 2010 at 9:03 AM, Bart Coninckx 
<bart.coninckx@xxxxxxxxxx>wrote:
> > On Friday 09 July 2010 09:29:09 Alex Edwards wrote:
> > > hello all,
> > >
> > > I have little experience of virtualisation only what i have read in the
> > >  past couple of days! but i think it can offer me what i need. I would
> > > be grateful for your input.
> > >
> > > I have 3 systems I need to demo, I want to deploy these systems to a
> > > base state where i know that they will be working. At this point I want
> > > to
> >
> > lock
> >
> > > them. I want to be able to give it at this point to somebody and say
> > > "do want you want" when/if they break it i want to be able to return it
> > > to
> >
> > its
> >
> > > known stable state. This return to a stable state needs to happen
> >
> > quickly,
> >
> > > seconds would be great but minutes would be acceptable.
> > >
> > > I have been reading about differencing disks and believe that these
> > > would be the right solution?
> > >
> > > thanks
> > > Alex
> >
> > I believe that is a sort of snapshotting you are referring to; AFAIK Xen
> > does
> > not have such a feature, but LVM does. You need to install your root file
> > system on LVM as well, don't know what the effect would be of restoring a
> > root
> > file system snapshot however. Also don't know if this can be done in
> > "seconds"
> > - you need to try this I think. Another way could be to make a RAID1,
> > disconnect it after your initial install, then after changes swap the
> > main disk and mirror it again to the first one to get to the original
> > state. This
> > answers the "in seconds" part.
> >
> > B.
> 

Forget about my remark about the root file system and the RAID1, was thinking 
of a physical machine. For Xen, I would do it like this:

- create a master image file
- copy this to in three versions: orginal.img, running1.img and running2.img
- boot the Xen machine with running1.img, have people change stuff
- stop the Xen machine, change the image file in the Xen config to 
running2.img
- start the machine again
- copy orginal.img to running1.img 
- stop the machine, change config to running1.img
- copy orginal.img to running2.img 
- repeat ...

scripted this will only take you seconds. It does suppose however that the 
guests are running long anough to have the original image copied in 
background.

B.


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