title: Why Disk image file on host computer doesn't decrease when I delete huge files in virtual machine?
body: <p>I installed CentOS on the virtualbox(Host OS is Windows 7). I created the disk image file that is VDI files(<strong>dynamically allocated image</strong>). Recently,when  I delete huge files in CentOS,the VDI file on my disk doesn't decrease. Why? How to tackle this problem?</p>