Virtualbox

VBoxManage

clonehd

This command duplicates a registered virtual hard disk image to a new image file with a new unique identifier (UUID). The new image can be transferred to another host system or imported into VirtualBox again using the Virtual Media Manager.

VBoxManage clonehd  <uuid>|<filename> <outputfile>
                    [--format VDI|VMDK|VHD|RAW|<other>]
                    [--variant Standard,Fixed,Split2G,Stream,ESX]
                    [--existing]

modifyhd

With the –compact option, can be used to compact disk images, i.e. remove blocks that only contains zeroes. This will shrink a dynamically expanding image again; it will reduce the physical size of the image without affecting the logical size of the virtual disk. Compaction works both for base images and for diff images created as part of a snapshot.

For this operation to be effective, it is required that free space in the guest system first be zeroed out using a suitable software tool. For Windows guests, you can use the sdelete tool provided by Microsoft. Execute sdelete -c in the guest to zero the free disk space before compressing the virtual disk image.

Please note that compacting is currently only available for VDI images. A similar effect can be achieved by zeroing out free blocks and then cloning the disk to any other dynamically expanding format. You can use this workaround until compacting is also supported for disk formats other than VDI.