Yesterday, I talked about the benefits of installing IBM products into VMWare. Today, I just want to mention a quick tip about how to retain the performance of your virtual machines.

When a hard drive is created in VMware, you have the option to specify whether the space should be allocated dynamically or ‘all at once’. If you allocated the disk all at once, there is nothing to shrink. If you do it dynamically, what you will see is that your disks grow and grow and grow until they reach their maximum size. They land up being much much larger than the sum total of the files inside the machine. This is due to some techno-babble about how operating systems mark files as deleted.

What the ‘Shrinking’ process does is wipe all of these deleted file allocations with zeros and then re-organize the disk to put the remaining files in order, thus, eliminating all the gaps (the extra wasted space). You will find at the end of the process that your VM is substantially smaller.

Also, because the disk is substantially smaller, it’s easier to VMWare to find the files being accessed inside the virtual disk.  I had a VM (WebSphere Integration Developer v6.0.2) that was chugging along very slowly. After I had defragmented and shrunk the disk, it was back to being lightning fast (and about 30% smaller).

I’m not sure what a good guideline is for shrinking your disks, but if you uninstall or reinstall a large software suite, I recommend doing it then. It will take about 20-30 minutes but you’ll get that back that time in faster responses.