I have a Windows XP host and a Windows Server 2008 R2 guest. When I leave the virtual machine alone overnight, Workstation slows to a crawl (with extremely heavy HDD access) when I try to interact with it again the next morning - clicking on something results in a 30 second delay before there is any sort of response. I have to completely shut down the VM (which takes about 20 minutes), wait a few minutes, and then restart the VM before performance is restored.
How can I prevent the VM from slowing down overnight?