I recently switch to VirtualBox (from VirtualPC), but i was not ready to dump all my VHD files. So i decided to keep working with VHD. The other thing I use a lot is “differencing disk”, VirtualBox also support these, but, as with VHD the documentation is not always very clear on how to use them.
First you have to understand a difference between Virtual PC and Virtual Box about “differencing disk” :
| In VirtualPC | In VirtualBox |
| You create a normal VHD that will become the parent, then you create a child VHD pointing to the parent | You create a normal VHD and flag it as “immutable”, then you create new VMs using this “immutable” VHD. VirtualBox will automatically create the child VHD that will appear like a snapshot ({GUID}.VHD) |
Here’s how I do it :
Step 1 : Create a 20Go dynamic disk VHD
vboxmanage createhd --filename "F:\.VirtualBox\HardDisks\WinXP_Parent.vhd" --size 20480 --format VHD --variant standard --remember
Step 2 : Change the new VHD into an immutable disk
vboxmanage "F:\.VirtualBox\HardDisks\WinXP_Parent.vhd" --type immutable
I Also like to force it to read-only as an additionnal precaution :
attrib +R "F:\.VirtualBox\HardDisks\WinXP_Parent.vhd"
Step 3 : Create a new VM using the WinXP_parent.vhd
Yon now have a new virtual machine with a differencing disk in the VHD format.
