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Backing up a Windows VM: Should You and How

by Kerry Dawson

Backing up is critical. It is one of those activities that is probably the most important maintenance routine you can do. It ensures that, as long as you have a good backup and really a good backup plan, that the file you accidentally deleted or even the disk that failed has recoverable data. Any other maintenance routine you do nor no recovery softare will guarantee what a solid backup can accomplish.

Not that it’s not important that you don’t run some kind of maintenance to keep your computer in good operational stead. It is very important although somewhat debated. The requirement to ensure you have a good backup though is not open for debate and is commonly accepted as good computer practice. What is debatable is the degree that you backup but that at least one backup is not even open for discussion. It’s essential.

A Robust Backup Strategy

In “A Robust Backup Strategy” I outlined the various natures and degrees of backup strategies that can be employed to ensure safety and convenience. To summarize, at a minimum you should have on two separate media one incremental backup and one clone backup. The incremental backup allows you to go back in time to find a good version of a file whilst the clone backup allows you to boot from the clone and get up and running fast. Further, with a clone backup you can, for sake of expediency, just re-clone your clone back to your hard drive.

For many these days, an offsite backup is being added to the mix in case there is a local disaster which could happen all too easily. There are some very good backup services now for the Mac which are reasonably priced.

Cloning A Windows VM

Cloing a VM is not extensively discussed but it is important and will become increasingly important as more Macs run Windows in a production environment which appears to be happening. The reason this requires discussion is the nature of a VM so in this case when I talk about a VM I will be referring to a Windows VM but it applies to any VM.

A VM is one humungus file seen by the file system as one complete file. In the case of a VM file they can be quite large. As an example, a standard Windows 8 VM with just a Office 365 installed can be 40 gigs in size. When you run Windows say on Parallels the file system sees the complete file as having changed. In an incremental backup, the efficiency of backup is obtained by the file system backing up only what has been identified as having changed. Thus, instead of huge files backing up say in a DB only the component parts of what has been changed are backed up saving large amounts of remote file storage.

Where it comes to a VM the whole file or in the case of the above example 40 gigs has been marked for backup. This is slow and takes a tremendous amount of remote file storage. If Windows were run daily, a daily backup of the system could exhaust the remote file store rapidly. Not only might some things not get backed up at some point, the number of incremental backups or backups through time is dramatically impeded.

Backing up a Windows VM is Essential Also but…

I don’t know if there is one good school of thought on this but this is what I recommend as the backup of a VM is as essential as that of the host VM.

On all your incremental backups be they Time Machine, Retrospect, Crashplan etc…. exclude the Windows VM from backup. It is this kind of backup that makes the backup inefficient and slow and uses a ton of disk space. On the other hand, have backup enabled on all your clone backups. This slows the backup down somewhat but it will not exhaust disk space. You will have a backup of the VM it just will not be incremental.

Should you want Incremental Backup of your VM’s Data

If you absolutely feel you must have incremental backup on your clone backup there are one of two things you can do. You can have a couple of rotating clones. This would at least separate say two backups by a couple of days or so.

Finally, you could employ Windows backup software within the Windows clone environment and it would have full functionality but through Windows. I would only do this if you use Windows extensively and absolutely need incremental backup for safety.

A VM Backup Strategy in Hand

With this, you have VM backup strategy in hand but one that ensures your have a backup of your data yet not one that a will exhaust ridiculous amounts of hard disk speed or Internet bandwidth.

It is just as important to have a VM backup included in your complete system as many things could happen. The VM might corrupt ruining your entire Windows environment. There could be a complete failure of your hard drive leaving you without any means of recovering your VM nor it’s data.

As with any backup, this an insurance policy you hope you never have to use. Should you have to though it will save you a tremens amount of time putting your VM back together and a lot of heartache being able to recover you precious data.

At this point it doesn’t make sense to question why you’re running Windows and thus have a virtual machine that needs backing up. There’s often more than one reason for the use of Windows on a Mac. What’s important is the VM is treated as a full operational system with important data that needs to be backed up should anything go wrong.

With a sound backup strategy that includes your Windows VM, you can sit back and relax knowing you’ve done your best to give yourself a healthy insurance policy. A congratulations is probably in order as you’ve protected your critical investment in your data. You’ll definitely thank yourself should anything go wrong and you have to draw on that investment.

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