Why does Virtualbox' virtual disk not grow automatically?

Solution 1:

We have no idea why Windows in your case can not handle the dynamically allocated virtual disk. It may be worth to check the filesystem integrity or perform a defragmentation from your Windows guest OS.

Nevertheless we can easily increase the size of a dynamically growing virtual drive reported to the guest OS by issueing the following command run in a terminal:

VBoxManage modifyhd <uuid/name> --resize <newsize in MB>

Replace with the uuid or the filename (full path needed) of your virtual drive. These can be listed with the following command:

VBoxManage list hdds

Note that obviously we can not change the virtual drive size if we had taken snapshots or saved the machine's state instead of power off. Before we change the virtual drive's size we therefore need to delete all snapshots, or work on a clone to makes sure we do not loose a snapshot's content. Shrinking a dynamically growing disk is not possible.

After having resized the virtual drive we will then have to adapt the partition table of the guest to altered drive's size.

In Windows 7 go to Computer Management -> Disk Management to view new unallocated space (shown after resizing with adding 10 GB to the drive):

Right click on this unallocated partition to select "Extend Volume..." to increase the partition size. You may also do this with booting an Ubuntu live .iso on this virtual machine to resize partitions using gparted.

More details here: Virtual Box User Manual

See also: How do I increase the hard disk size of the virtual machine?

To physically shrink/compact a dynamically growing disk see: How do I shrink a dynamically growing VDI disk from VirtualBox?

Solution 2:

You could have added a 40,04GB growing disk, but the Windows partition itself should have been created with the full size at installation time.

Add a Ubuntu CD to your virtual machine and boot with it. Launch gparted on the dash. Open the disk.

You should see a 40,04GB partition and no free space. If you see a smaller partition and free space, use this own tool to resize and grow the existing partition.

After resizing and restarting your virtual machine, Windows will do a partition check, please let Windows do it at least this time! It's important. Don't worry too much about your data though, it's a normal procedure when resizing NTFS partitions.