In resource monitor, the disk activity tab double-counts I/O against the device of a mounted VHD.How to reproduce: mount a VHD, and start doing heavy writing ( for example copy a large file on the vhd to the VHD )on that VHD. In resource monitor sort the disk activity tab by Total B/Sec. You,ll see that Image 'System' counts activity against the VHD file, and Image 'Your Program' (or System if you're doing a file copy) show approximately the same numbers against \Device\HarddiskVolumexx. Those numbers are also added up in the MB/sec Disk I/O count, resulting in figures which my disk system can never attain. (It's giving me an average of 60MB/sec, while the disk subsystem is rated at 30 30MB/sec)