virtualbox.org

the host's got plenty space, the VDI is dynamically allocated (at least thats how I set up in VB), the real capacity now is near 4G, but the VDI itself can reach up to 8G the running out of free disk error happens when I tried to update Ubuntu guest, I can't see any other reason stopping me from doi...

I've got not enough free disk space error message on ubuntu guest on windows 8 host despite I've set up dynamically allocated VDI, how to go around this?
the windows 8 host is of NTFS