The solution was to disble the service "Superfetch". Hey presto, all is quiet again.
Superfetch was trying to keep my system running fast by pre-loading the VHD into memory. Madness.
I've had superfetch turned off all day, and my hard disks's have never been so quiet.
Now, if only there was a way to exclude folders from superfetch...
Having a Google around there's no exclusion list, however, there is a way to refine what's going on via the registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters
Modify the EnablePrefetcher key to one of the following settings:
- Disable Caching: 0
- Cache Applications Only: 1
- Cache Boot Files Only: 2
- Cache Everything (default): 3
Experiment with this key to see if caching applications or boot files rather than everything still provides enough of a performance boost without getting bogged down.