How To: Increase VirtualBox Hard Disk Size

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Assuming that you are running a Virtual Windows (WinXP, Win7, ...):

1. Export the Virtual Windows as OVA.
2. Import the OVA and select the option "import hard drives as VDI".
3. Exit VirtualBox Manager.
4. Using Console Window, run command: (Assuming the disk name is disk1.vdi and you want to resize to 40GB)
1. BoxManage modifyhd "disk1.vdi" --resize 40960
5. Start the Virtual Windows.
6. Using Console Window, run command:
1. diskmgmt (Windows Disk Management Application)
7.  Right-click the existing Allocated Space and select Extend Volume. Select the Unallocated Space as the target.