VBoxManage modifyhd --compact

VBoxManage modifyhd --compact crashes or corrupts .the vdi image
There is a bug in VirtualBox 2.2.2 which is fixed in later releases. Don't use this command with release 2.2.2 or your .vdi image might get corrupted!

User_FAQ – Oracle VM VirtualBox

知らずに使ってしまったが、幸いVDIファイルは壊れなかった。