All is normal when Fences is disabled, but when I activate Fences there is a strong hard drive activity on "Datenträger D:" this means "Hard Drive D:" where Windows 8 is installed. Sometimes the activity runs about minutes.

My System:
Windows 8 x64 installed on hard drive D: as VHD
Asus P5P43TD Pro
Intel Core 2 Quad Q9650 3.00GHz
ATI Radeon HD 5850 1GB
Corsair XMS3 3x 4GB DDR3
Creative Audigy 2 ZS
Samsung SH-S222A