ever stuck in this situation where you need to increase virtualbox disk size and don't want to re-install everything on a new virtual machine?
Well its supereasy to increase the size of an existing disk, follow these steps:
1. Create a new virtual disk with the desired size (fixed or dynamically expandable as you want it).
2. Go to settings of your actual disk and open storage section
3. Mount the newly created disk as slave
4. Run/boot actual disk (now your newly added disk shoudld be avalibale as another drive)
5. Now you can easily clone your actual disk to the newly added disk using following applications available for windows (I use Archonis Easy Migrate Trial ) or google a similar tool for linux.
-Arconic easy migrate
-Drive Image XML
6. Now mount the newly created disk as the primary disk to your virtual machine and reboot.
thats it..you are done.enjoy