Victoria House wrote this in a Defrag question post:
There is a default maximum allowed shadow storage space (15% of volume), so
you needn't fear your free space decreasing until there's none left.
-Victoria
Can the space be increased above 15% of volume on each disk volume in Vista
as one could do in XP?
Note: thanks to MSFT experts such as Victoria, and others for making this
group very productive and useful.
Microsoft Windows Vista