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So why would you want to run your desktop in a VM?

There are many reasons. Most of them have to do with the way that Virtual Machines aren’t connected directly with the hardware they run on.

1. Virtual Hardware: By virtualizing the actual hardware away, gone are the days of searching for funny drivers. You can make every VM use the same virtual hardware.
2. Easy, complete, full, backup. Since the VM is just 1 or 2 files on the disk of the host, backup is as simple as shutting down the DomU and copying the file(s) off to another media. You can burn a 20GB image to DVDs, CDROMS, or just copy it over a network to another box. There are 3 ways the disks can be setup
   1. Raw disk access – you create a partition outside the normal Dom0 disks and place the DomU filesystem their. This will provide the best disk performance since you are using just a very thin layer between the DomU and Dom0 disk system.
   2. Pre-Allocated Disk – this is a file that is pre-allocated to the maximum size requested. If you ask for 20GB, then the file size is 20GB to start. The performance is good since Dom0 won’t be modifying that file as it grows. The bad is that when it comes time to backup the file, it will be 20GB even if you are currently using just 1GB of space. Compression should reduce this greatly for backups, but that is just an extra step you’ll want to take.
   3. Automatic growth Disk – this is the most efficient from a disk use perspective, but the worst performing for the disk subsystem. Backups will be just a tiny bit larger than the actually used space. For trying out VMs, this is usually the first way to go since it doesn’t require a big investment in disk or backup effort.
3. Easy full, complete, restore; Since you backed up the COMPLETE VM, restoring that file under another VM host will put you back to exactly where you were with all settings intact. Your laptop gets dropped in the airport before the largest meeting of your life? No problem, buy another at Best Buy and load your VM overnight from your backup. When you startup the DomU, everything is just as you left it. Emails, contacts, programs, and data. Everything.
4. Snapshots – these are internal backups managed by the virtualization host. I create a snapshot before installing a new program or going on a trip or trying a new driver. If anything goes bad, I drop back to the old point. Imagine you’re going on a trip where internet connectivity may be forced through undesirable hotel connections. Virus risk is high. Do a full backup before you leave home and a snapshot before you hop on that network. Any issues? drop back.
   1. Think about that just a little. You can go back to where you were … afraid of viruses? Create a snapshot – do the dangerous thing, then drop back. No worries.

What’s the downside?

1. Complexity – obviously, setting up Dom0 and DomU isn’t as easy as setting up a normal PC. However, once it is setup, you don’t need to know very much about it. Don’t forget to backup your DomU.
2. Possibly performance, but probably not. This is less of an impact now that new CPUs have virtualization hooks in them. You probably just need to enable them in the BIOS of your system before booting.
3. High End Gaming – Yep, if you run games that need direct access to the video card, then VM isn’t for you. However, if you run Real-Time Strategy Games or games from 5 years ago, then at lease VirtualBox has you covered.
4. Higher Hardware Requirements. This is true. You’ll need more disk, more CPU and definitely more RAM to use VMs instead of not. Let’s look at each of these.
   1. More Disk – a VM needs another copy of your OS. Everything else related to disk is the same as what you’d need to run the programs and have the data without a VM.
   2. More CPU – Just a tiny bit more, say 5% so I wouldn’t worry about this. Modern PCs with dual core CPUs are faster than you can use except for video editing. Well, if you’re running Vista, call that 10% – it really is a hog.
   3. More RAM – this is the biggest issue. Unless your computer has 4GB or more of RAM, you will probably need to be careful running VMs. I’m setup with 2GB for Vista and 2GB for WinXP on my DomU. My main concern was giving each DomU the amount of RAM is needs for the workload I perform. No more, no less. Vista on Dom0 will get whatever is left, but no less than 512MB. A Dom0 with resource problems isn’t good for any of the other domains.

The Future

I plan to load Ubuntu Hardy on my laptop soon, but that OS runs very nicely with just 256MB of RAM and 5GB of disk.

I may setup DSL and PuppyLinux DomUs too, just to have them for family and friends who’ve never seen Linux. They each run with 64MB of RAM and 150MB of disk. With checkpoints, I can let them go crazy in the DomU and drop back to a fresh startup when they are done.

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