On my previous article, I touched base with the types of VHDs that are available. I will now try and pinpoint which are the best scenarios to use each of those VHDs.
Fixed disks are the ones that offer the best performance because there is no dynamic creation since the VHD is always the size that was specifed in its creation. The chance of fragmentation is also less when working with Fixed VHDs. If your application is disk intensive and you are planning on running it on a VM, then this type of disk is the best way to go.
Dynamic disks work best when you want to make the best use of your space and you can withstand the performance penalty and fragmentation chance that can happen. If you want to save the most space when running VHDs, then dynamic disks are your best option. Use caution when working with dynamic disks as if the disk is expanding and the server runs out of space, disk corruption may occur.
Differencing Disks are a blessing for the IT Pro. If I was an IT admin, I would just have base VHDs of the most frequently used OS in my enterprise. For instance, I would have various VHDs with Windows Server 2003 Enterprise, Windows XP, Windows Vista and so on. When someone requested a Windows XP disk with Visual Stuido installed, I would just create a differencing disk and install Visual Studio. You can also have differencing disks of differencing disks which can become more and more useful in the long run. The main thing to watch out for is to make sure that the parent is always read only, since any modification will render the “son” VHDs in an unusable state.
Finally, if you are looking for a way to convert a physical disk that does not contain an OS, you can just link the physical disk to a virtual one by setting up a Linked VHD. Once you do that, all it takes is a trip to the Virtual Server Administrative interface and convert the linked disk to a fixed or dynamic one. If you want to convert a physical disk that has an OS installed, you must use the Virtual Server Migration Toolkit. Tips on how to use this tool belong in a future blog entry. Take care!