Resizing Ubuntu image to 40TB renders it unusable

[georgevreilly]

I had a 12GB VDI that was growing full, so I expanded it with

VBoxManage modifyhd Precise\ Pangolin\ 64/Precise\ Pangolin\ 64.vdi \
  --resize $((40 * 1024 * 1024))

I inadvertently asked for 40TB instead of 40GB. I was no longer able to use that image. Ubuntu would show a GRUB screen then abort with a disk error. I assume the file system in the VDI was ext4.

I tried to use modifyhd --resize to shrink the image down to 40GB, but VBoxManage refused to resize it.

Please sanity check --resize arguments.

[Klaus Espenlaub]

There is no way to sanity check <code>--resize</code> arguments in the way you expect it. After all a 40TB image is perfectly valid for VDI, as it supports up to almost 4PB. You're apparently bumping into a limitation of grub, freaking out on such large disks.

It is right now an intentional limitation of <code>modifyhd --resize</code> to refuse shrinking an image, because this operation can easily lead to data loss, for very similar reasons as you bumped into: getting the scale wrong.

There are ways to create a new disk image with the old content (actually the new size can be bigger or smaller with this recipe): ​http://alittletothewright.com/index.php/2009/11/expanding-virtualbox-dynamic-vdis/