Resizing disk fails for macOS guest

[zambon]

I tried to resize a 20 GB VDI disk to 40 GB using VBoxManage, and that didn't work as I expected. I'm not entirely sure which component failed, but I decided to post this as a bug here. Please find the details below.

Environment

VirtualBox version: 5.1.22 r115126 (Qt5.6.2)

Host OS: macOS Sierra 10.12.4

Guest OS: macOS Sierra 10.12

Steps to reproduce

The following steps assume that a macOS Sierra 10.12 VM with a 20 GB disk (VDI) already exists in VirtualBox.

1) Resize disk.

VBoxManage modifymedium disk \
  ~/VirtualBox\ VMs/macOS\ Sierra\ 10.12/macOS\ Sierra\ 10.12.vdi \
  --resize 40960

2) Boot VM to expand the filesystem.

Results

1) The VM's storage settings for the disk indicate that the disk is now 40 GB - as expected.

2) The guest OS still indicates that the disk is 20 GB.

Workaround

Cloning the disk after resizing it, and then replacing in the VM's storage settings worked. I used the command below to clone the disk.

VBoxManage clonemedium \
  ~/VirtualBox\ VMs/macOS\ Sierra\ 10.12/macOS\ Sierra\ 10.12.vdi \
  ~/VirtualBox\ VMs/macOS\ Sierra\ 10.12/macOS\ Sierra\ 10.12.clone.vdi

Please let me know if you need more details.

[Socratis]

Please take a look at ​How to resize a Virtual Drive with HFS+. If you have to, continue the discussion in that thread please.

[Frank Mehnert]

I'm quite sure that the disk resize was successul but the guest OS somehow did not detect the new size.