Using a static disk, or even just multiple disks, within Parallels can make a big difference to performance. This is particularly true with Windows virtual machines within OS X; I’ve managed to change the boot time from about 30 seconds to under 20 just by changing to a static disk for VM. The default disk in Parallels is an expanding type – this saves disk space, because Parallels automatically adds to the size of the disk as you need it, but it also means that Parallels has to manage the allocated disk space, adding to the file used. Not only does the management imply a small overhead, there is a much larger chance of the file being fragmented. A more annoying effect is that the constant use of the expanding disk with virtual memory under Windows, means that size of the disk may increase just because you opened a large application once. You can get round this by creating a statically-sized disk, and then setting the virtual memory within your virtual host, to use this statically sized disk. To do this:

1. Shutdown your virtual machine – you cannot do this with a machine in the paused stated, because you are effectively adding new hardware to the machine.
2. Click Edit to edit the configuration for the virtual machine.
3. Click Add, and select a new hard disk
4. Unclick the Expanding checkbox and set the size; probably 1-2GB is fine, but keep in mind you will lose this amount of disk space permanently, even if your VM doesn’t use it all.
5. Save your configuration.
6. Start up your VM and configure the new drive.

For Windows:

1. Log in as a user with Administrator privileges.
2. Right click on My Computerand choose Manage.
3. Choose Local Disk Management.
4. Create a new partition/volume.
5. Once the new disk is ready to use, right click on My Computer again, and choose Properties.
6. Click the Advanced tab.
7. Click Settings under Performance.
8. Click the Advanced tab.
9. Click Change under Virtual Memory.
10. Reconfigure the VM settings, creating the new settings for the new drive (I recommend a lower value of 50MB and an upper value 2-10MB below the maximum size of the disk. Windows will use the minimum and dynamically increase it’s usage up until the maximum.
11. Remove the VM configuration for the original system/expanding disk.

You should be all set.It’s probably a good idea to run the Parallels Compressor and reduce the size of your disk now that you are no longer using the disk for virtual memory. For Linux, Solaris and other Unix variants you might want to run, the process is of course slightly different. For some environments, there are other benefits, but I’ll cover that in a separate post.