There has been some confusion going around as to the best way to back up data in a VMware Fusion virtual machine.

It is not practical to use Time Machine to back up the entire virtual machine as the virtual disk (the .vmdk file in the virtual machine bundle) is generally quite large, often 10’s of gigabytes. Simply booting the machine and shutting it down again, without actually doing anything will mean that Time Machine sees the entire virtual disk as being modified and it will try to back it up again. This causes a number of problems, the main ones being:

* Time Machine may not ever get a complete, working backup of the virtual machine
* Time Machine runs out of disk space quickly
* If using Time Capsule over AirPort, your Time Machine backups will swamp even an 802.11n wireless network

I am of the habit of storing all my virtual machines in the one folder (VMware defaults to using _~/Documents/Virtual Machines_) and specifically excluding this folder from Time Machine backups completely. As an aside, if you also use Entourage it’s recommended to not back up the Entourage database in _~/Documents/Microsoft User Data/Office 2008 Identities_ folder for much the same reason.

h3. How do you back up your important data in VMware?

This is a good question, and it depends on the amount of data that you need to back up. As a sweeping generalisation, one of the widest uses for VMware Fusion is to run a Windows-based accounting package on the Mac. The fact is that there are a lot more good accounting packages for Windows, and they’re a lot more widely supported by accountants. MYOB is one example where even though there are a couple of different Mac versions, you have nowhere near the choice that you do on Windows. QuickBooks is another – there’s a Mac version in the USA, but not in Australia with Aussie tax tables.

In this case, you can happily run your accounting package in Windows, and it will usually run very well indeed, and use the VMware _Shared Folders_ to map a folder on your Mac into the Windows environment. Once this is done, then in Windows configure your software to save it’s backups to the shared folder (which will probably appear as being on the Z: drive) and you are then backing up directly to your Mac. Ensure that this backup isn’t going into the Virtual Machines folder (I’d recommend something like your _Documents_ folder) and then these backups will be captured by Time Machine and backed up properly.

Once these processes are in place, you can make manual backups of the virtual machine on an ad-hoc basis as other than your accounting data, very little will tend to change in the virtual machine over time. You will need to ensure that when backing up the virtual machine (by dragging it’s icon over to an external drive, for instance) that it has been shut down properly, not just suspended. This will ensure that you have a copy of the virtual machine that is in a consistent state and can be re-deployed if something happens to the original.