VMs won't start hanging with msg "Starting virtual machine - 0%"

[Eugene San]

On fresh Ubuntu 16.04 with VirtualBox 5.0.16 virtual machines won't start hanging with msg box "Starting virtual machine - 0%".
The issue is not persistent but once it happens to specific virtual machine, that machine won't start anymore.

Observations:
- Affects both build from Xenial repo and Oracle package
- Both Linux and Windows virtual machines affected but Windows machines cause heavy I/O until all VirtualBox processes are killed
- Tested on Skylake and Sandybridge machines
- Downgrading to 5.0.14 doesn't help
- Removing extensions pack doesn't help
- libvirt@qemu-kvm is working ok
- Nothing useful in log but attached anyway
- No suspicious massages in dmesg

Might be related to system being installed on BTRFS.

P.S.
The issue indeed replated to BTRFS. VirtualBox do not handle COW correctly:
- http://superuser.com/questions/623989/virtual-box-stuck-at-starting-virtual-machine-0
- https://www.virtualbox.org/ticket/11862

[Eugene San (eugenesan)]

Attached script for fixing "broken" VMs.

[Gianfranco Costamagna (costamagnagianfranco)]

thanks for the bug report, please ping upstream about a timeframe or fix :)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.