PVM file size change dramatically in Parallels 6

I have just upgraded from Parallels 5 to 6 for Mac Lion. But I have noticed that the PVM file changes size dramatically every time I start Windows XP VM.

When the VM is off, the PVM file is about 20MB; when the VM is on, the PVM file changes to about 3GB; when I turn the VM off, the PVM file changes back to 20MB. Is this normal? If it writes to the disk with that big amount of data, it is going to kill the SSD very soon. Any way to fix it?

Thanks.