Re: [Xen-users] differencing disks

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Fri, Jul 9, 2010 at 2:29 PM, Alex Edwards <edwards.alex@xxxxxxxxx> wrote:
> 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?

Sort of, though I'm not sure if the term "differencing disk" is often
used in Xen.

In Xen (the open source hypervisor), when using Linux dom0, you could
use LVM snapshot like Bart mentioned. This is Linux LVM feature, not
Xen-specific feature. IMHO it's kinda tricky to use though, since it
uses somewhat different concept (e.g. "rollback" might not be easy).

Xen 4 internally has support for qcow and VHD
(http://lxr.xensource.com/lxr/source/tools/blktap2/README). Hopefully
others can share their experience using it.

There's also XCP 0.5
(http://blog.xen.org/index.php/2010/07/07/xen-cloud-platform-0-5-released/)
with live VM snapshots & checkpoints feature, which you might want to
look at (although I haven't used it personally).

If you're feeling "adventurous", you might want to also check out
storage-based snapshot/rollback/clone with zfs, which is possible
using
- freebsd/opensolaris dom0 (dom0 support might not be as good as Linux dom0)
- linux dom0, with zfs-fuse

If you're new to virtualization, and use it primarily on laptop for
testing/demo, I'd actually suggest you do not use Xen, and rather use
virtualbox/vmware. Also note that whatever method you use to provide
snapshot/rollback capability, it will incure some kind of overhead
(which can be significant), so be sure to test it first.

-- 
Fajar

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