First available in Windows 2000, Dynamic Disk is feature that, among other things, can act like a software RAID. It allows you to have multiple disks appear as one, which can then include an unlimited number of volumes. This can allow you to better organize your files, improve file performance, and if the right options are used, even protect your data against loss due to drive failure. So what’s the problem?

One problem with Dynamic Disk is that it doesn’t work with all versions of Windows. Windows XP Home Edition doesn’t support them, presumably so you’ll spend more for XP Professional if you want to use the feature. Does that mean you can use it if you’re using XP Pro? Not necessarily. If you are running on a mobile computer, it’s disabled with the presumption that there aren’t multiple disks in your laptop, so you shouldn’t need it. Another limitation is the type of disk you have. Dynamic disk cannot work on Firewire, USB or removable disk (at least in earlier versions of Windows, I was able to convert a Firewire drive in Vista Ultimate). Want to use the mirror or RAID-5 features to protect your data against disk failure? That only works on Windows 2000 Server or Windows Server 2003.

What about Windows Vista? Windows Vista does work with Dynamic Disks as well. Sometimes. I think. This Microsoft Help article, about basic and dynamic disks, is said to apply to ‘all editions of Windows Vista’. This would seem to imply that dynamic disks are available to all versions. Browsing around the internet, I’ve found many stories of people who upgraded their systems to Vista only to find their dynamic disk unavailable. My best guess (since I cannot find ANY Microsoft documentation stating otherwise) is dynamic disks are only available in Vista Business, Enterprise, and Ultimate. Unless your using a laptop of course.

What’s really unfortunate is that neither the Upgrade Adviser, nor the Vista installer itself will warn you if you have a dynamic disk that won’t be readable after the upgrade. So if you’re running Windows XP Professional and have a dynamic disk, and you upgrade to Windows Vista Home Premium, you won’t be able to read the dynamic disk. The good news is that you can convert the dynamic disk back to a basic disc, the bad news is that it will erase all the data in the process (there is a hack that supposedly works if your dynamic disk doesn’t span multiple disks).

So if you’re running Vista Ultimate you can almost certainly use dynamic disks right? Maybe not. Though Ultimate understands your dynamic disk, and the Media Center software understands it, if you use Media Center Extenders, like an xBox 360, they cannot. So if you want to take a bunch of disks and put them together into one large disk where you plan to store all your videos, better think again if there’s any chance you’ll ever use an extender.

Dynamic Disks sound like a great concept. It’s to bad that marketing decisions and compatibility issues make them such a risky proposition. Sure, you might have them working fine now, but will they survive an upgrade? Could something as simple as a poorly coded hotfix deny you access to them? I’m sticking to the standard basic disks as I’d rather not find out.