RE: [Xen-users] differencing disks

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> 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?
> 

Is it DomU systems you want to do this with, or the whole physical
machine? If DomU's, are they Windows or Linux? Windows has Microsoft
SteadyState so you wouldn't need to even involve Xen in doing this, and
the user could control if their changes are written back to the 'base'
or not at shutdown time. I'm sure Linux has CoW (Copy on Write)
filesystems which would also allow you to do this without involving Xen
too, which is probably best if you are just learning.

Is there no such thing as a 'snapshot' block device handler? Eg
'snap:vg-xen/lv-linux-domu-base' which would create a snapshot of the lv
(maybe using domid to make the snapshot name unique). That would be
really useful!

James



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