virtualbox.org

I want to increase my virtual os disk size,so I do this:

D:\Program Files\Oracle\VirtualBox>VBoxManage modifyhd "C:\Users\right.zhang\VirtualBox VMs\Win8\Win8.vhd" --resize 30000
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%

Then The virtual os(win8) can't be started,It show me
FATAL:No bootable medium found! System halted.

How can I do to recover my virtual os?

I'm not sure if Win8 still does this, but possibly you were using a Windows dynamic disk (not to be confused with VirtualBox Dynamically Allocated disks), in which case it hides a partition database up at the end of the disk. Of course if you resize the disk then this database is no longer where it should be.

The only possible cures are: restoring the damaged VDI from a recent backup, or hacking the VDI header to reduce the disk size.

I hope you are aware that this method of resizing does not work if you use snapshots, although the exact effect depends on what you do next.