No doubt you have tried using Virtual Machine technology to allow extra services within your school.  For example you wanted to try Moodle, or perhaps setup a test web server to try something out.

I use virtual machine images all of the time, for my application development work, or even connecting into my works network via a VPN.  Without the use of Virtual Machines, my computer would be full of junk that would just clog up the computer.  They are really helpful when you don't have resources for setting up multiple machines for specific tasks.

All of these Virtual machines take up disk space one way or another.  VMWare (www.vmware.com) has the ability to split virtual hard disks into 2GB chunks, this helps with keeping file fragmentation down.  Where as Virtual Machine (www.microsoft.com/virtualpc) uses a single huge file to store is data on.  Regular use of Virtual Machine will eventually mean that your disks become fragmented, slowing down the performance of your PC and Virtual Machines.

Defragmenting the Virtual Hard disk images will take ages to complete, as they are so large.  You will also need a stack of disk space to store the images on.  I mainly store my images on separate hard disks from the host operating system.  I have some VM's running on a USB2 disks and the main images that I use all of the time run from an External E-SATA drive - ensuring top performance without impacting on the host OS.

Microsoft Virtual Machine has a Disk Compactor tool built in, this is supposed to release all of the unused sections of space in the Virtual HD file.  To be fair it does a reasonable job, and the image size is reduced.  But this is a process that you have to undertake yourself.  It is a time consuming process to compact the images and defragment them.  The same is true with VMWare.

The answer to managing the size of your Virtual Machine Images is to use an application from www.visioncore.com. vOptimizer will process any of the VM Images that you have and does its best to remove all of the redundant data from the image.  This includes removing temporary files and OS features such as the games in Windows XP.  There are 21 optimisation features that are user selectable.

The good news is that VisionCore have a freeware version of the application http://www.vizioncore.com/voptimizer/voptimizer_freeware.html perfect for managing your VM images.  There are comercial licences should you have requirements to optimise images stored on remote drives.

Testing vOptimizer, gave really good results, one 12GB Windows Server 2003 images was reduced down to just under 9GB.  The same was true of a Windows XP image.  This 3 GB space saving should really make a difference when backing up the images and also with the everyday use of the Virtual Machine.

The ban news with vOptimizer is that it will only work on Windows based Hosts with Windows Operating Systems of Windows 2000 and above installed.