Resize an existing Dynamic VirtualBox .vdi Hard disk

You created a VM in VirtualBox and now you find that you've hit the limit on maxmimum disk size. You need to resize your VDI hard disk. There are a lot of conflicting advisories on how to do this, many of which are quite complex. Actually it is very simple:

Using the VBoxManage command line utility that is in your VirtualBox installation folder, execute the following command:


VBoxManage clonehd --existing  I:\VirtualBox\win2008R2x64.vdi   I:\VirtualBox\win2008R2X642.vdi


where I: is the drive letter,  win2008R2x64.vdi is the name of the original VDI hard disk file, and  win2008R2X642.vdi is the name of a new, larger dynamic VDI hard disk that you have already created using the VirtualBox GUI via File/Virtual Media Manager.

The key is the use of the "--existing" switch. Without this, VBoxManage will error out complaining that the target VDI file already exists.

Once you have switched to the new VDI disk and started your cloned OS, go into the Disk Management snap-in and Extend the volume to occupy all the new free space.

Done!