Hey Parallels: I've got a base vm that is about 8 gig in size. I'd like to have multiple copies of it, to do various things with, but I don't want to have lots of copies of it laying around, filling up my disk. What I'd like to see is a base VM image that is used in ReadOnly mode by multiple VM instances, each with a separate 'after image' (AI) file where updated blocks are written. The logic for reads would be for the VM instance to look first in its AI for blocks and then in the RO master copy. The logic for writes would be to always write in the AI. This would be handled by the virtual hardware of the VM and would be transparent to the guest OS's. This would allow me to have several different instances of VMs without using so much disk space. It would make performing incremental backups of VMs extremely doable. Once the master VM is copied to the backup dest, only the AI files that have changed would need to be backed up. Tools like rsync would work well with this approach. Ultimately, I'd probably also want a copy tool which would create a new, merged VM copy of the master VM and an instance's AI.
