Immutable differenced disks

[Doktor Jones]

Is it possible to make differenced disks immutable?

Here's the scenario:
1. Create an initial immutable disk (disk 1) with a stock Windows XP installation + IE 6
2. Create a differencing disk (disk 2) off disk 1, attach it to a different VM, and install SP2 and IE 7
3. Make disk 2 immutable
4. Create another differencing disk (disk 3) off disk 2, attach it to a third VM, and install SP3 and IE 8
5. Make disk 3 immutable

The goal is to have three separate VMs, one running base XP, one running SP2+IE7, and one running SP3+IE8, with all of them immutable. I don't want to fully duplicate the images, because that seems like a lot of wasted disk space on XP system files. Is this possible, and if so, how?

Also, I'm looking at adding IE9 too, for a fourth VM...

[mpack]

What you describe is basically the same as snapshots - and its an open invitation to disaster, as a fault in your base drive kills all three.

IMHO: go ahead and waste disk space. If that's a concern then buy more disk space.

[Doktor Jones]

What you describe is basically the same as snapshots - and its an open invitation to disaster, as a fault in your base drive kills all three.

IMHO: go ahead and waste disk space. If that's a concern then buy more disk space.

1) These are testing environments; in the highly unlikely* event that a fault DOES occur, boo hoo, I'll recreate them. The entire point is to NOT retain data, other than the base install
2) My money does not flow as freely as water; most of it goes towards food in my mouth and a roof over my head, I can't just "buy more disk space" at a whim

*in my experience and general opinion

[mpack]

Absolutely, it is your choice to make.

If you don't care about data integrity then go ahead and set it up using branching snapshots as I said. If you prefer the exact mechanism you suggested, I've not tried it, I don't know who else could advise you with certainty, so why not just try it? I don't see why it shouldn't work - the underlying disk routines are the same as when branching snapshots are used, so I don't see why you would see any extra constraint.

Btw, on disk space. In most peoples cases, disk space is cheaper than the time they lose working around the lack of it. Also, with independant clones your main disk need only contain the VM you need for testing today, leaving you with more on your main drive: you could have a large number of independantly moveable test environments all stored on something like a WD passport drive. With your technique you've essentially welded all your test tools into one inseparable lump. I'm not convinced that is the most convenient form a set of tools can take...

[ edit: corrected typo which was annoying me ]

[Technologov]

Unfortunately this is not possible with VirtualBox 4.0 AFAIK.

However it was possible with VirtualBox 3.2 (altough not officially supported).

See here.

I suggest you this:
Try this on VBox 3.2.x, then complain on vbox-dev mailing list to re-add this feature.

I don't complain, because I use only one level of hierarchy. I.e. only single shared immutable image across all VMs.

-Technologov