Re: Fwd: [Xen-users] differencing disks

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

On Friday 09 July 2010 12:05:30 Alex Edwards wrote:
> Yeah thanks Bart thats what im after. Would i be potentially be able to run
> running1.img and running2.img at the same time? And i can build something
>  in that will prevent it from trying to start an img thats being copied but
>  i dont forsee it being that unstable that it breaks that often.
> 
> thankyou very much
> Alex
> 
> On Fri, Jul 9, 2010 at 10:57 AM, Bart Coninckx 
<bart.coninckx@xxxxxxxxxx>wrote:
> > 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.
> 


Well you can't copy and use an image file at the same time obviously. If you 
are running several guests at the same time, you just need to repeat this 
procedure per guest. 

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