Quoting from MacDailyNews

PD Tweaker is an Application Enhancer (APE) plugin that addresses a few shortcomings in Parallels Desktop 1.0 for Intel-based Macs. Parallels Desktop for Mac gives Apple users the ability to run Windows alongside Mac OS X in a secure, isolated virtual machine.

PD Tweaker has two major features which can be enabled separately:
• Optimizes caching for HDD and SAV files: A much better caching strategy for these files is actually no caching at all. Caching large files is actually harmful to your Mac's overall performance. HDD files do not need caching because the client OS will already have a cache layer. SAV files are streamed in and out and don't need to reside in the disk cache.
• Always writes HDD and SAV files all the way to disk: Your data is precious. Especially data like a HDD file that took you hours to install and configure. Shouldn't you treat it that way?

Developer Drew Thaler says, "I'm sure that eventually they will incorporate these features into a future version of Parallels Desktop. But in the meantime, I just really needed to run Parallels without paging up a storm. I fully expect PD Tweaker to be obsolete very soon, but I just thought I would share. Who knows, maybe it'll light a fire under them to fix it sooner."

More info and download link (Unsanity's Application Enhancer 2.0 or later also required) here.

The original article is here.