Mac - Fix virtualbox disk image in OS X

I installed the latest virtual box on a mac book.  Since i want my virtual machines to be runnable from multiple machines, I have the disk images installed in an external hard drive.

Here the problem comes, mac can read-only a ntfs drive, but cannot write to it.  So i reformatted the drive to win32.  I didn't want ext64 coz it's still new and maybe unstable.

when i created the disk, i used the default disk type:  VDI, which grew when i installed ubuntu into it.  Once it reached 4GB, the OS hanged, because the VDI didn't split into chunks for win32.

little googling told me that VMDK does.

i don't want to reinstall linux on a new VMDK drive.  searched again on the net and found someone sharing the disk type conversion method:

VBoxManage clonehd "***.vdi" "***.vmdk" --format VMDK --variant Split2G

"tada!"  and it works like a charm