VMware Fusion and TimeMachine

Been a while since I blogged; swamped in work. This quick post to share a solution I found on Mac OS X to make VMware Fusion (or Parallels) and Apple's Time Machine backup work better together. I use a fair amount of virtual Windows and Linux machines, and these tend to be primarily stored in large virtual hard disk files - 40GB, 60GB,... pretty massive. Because Time Machine finds and copies any modified file, and the mere act of running the virtual Windows machines caused these large files to be marked as 'modified', I was faced with endless copies of massive virtual hard disk files to my Time Machine hard drive. Figuratively speaking, a one-byte change in one of those massive Windows virtual hard disk files would cause a 60GB copy operation - which also indirectly forced older backup files to be erased from the Time Machine drive to make room for these behemoths. Initially, I put all my virtual machines in a single folder, and explicitly excluded that folder from the Time Machine backup - not a good solution, but at least, my backup drive was not swamped with those big files. But then, a few days ago it dawned on me - I could have my cake and eat it too! The solution is to use the 'snapshot' feature of VMware (Parallels also has it) - you can make a snapshot of a virtual machine, so you can always 'undo' whatever happened to that virtual machine since the last snapshot. The way VMware handles this is by 'freezing' the underlying virtual hard disk, and storing any changes made since the snapshot to the frozen hard disk in separate files. And that's the solution: I first make sure my virtual machine is in a useful, stable state, and then I make a snapshot (I call it 'Base'). That effectively 'locks' the massive many-GB virtual drive - so running VMware does not cause it to be modified any more, and any changes from then on are kept in a bunch of much smaller snapshot files. Time Machine now makes a copy of my 'frozen' many-GB virtual drive once, and from then on only backs up the changes that are kept in the snapshot files - which results in a much smaller backup set. After a while, when the snapshot file size grows to many GB in size, I make a new snapshot, and delete the old snapshot. That 'merges' all changes that occurred 'between' the two snapshots into the main virtual drive, and starts with a fresh slate. After I do that, Time Machine backs up the behemoth once again, and from then again only backs up the changes in the new set of snapshot files. I now have a good backup of my virtual machines again without having to jump through hoops! Cheers, Kris

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