I'm very happy to announce that VirtualBox now supports shared disks. Finally we can attach one disk to several virtual machines and run Oracle RAC and other clusters. As Oracle promised, this feature is released with the next maintenance patch (thanks!).
There is a new image write mode which is called shareable and this options is now available for the commands createhd and modifyhd of VBoxManage. To create new shared image use the command VBoxManage createhd with type shareble, creating shared disk from the GUI is not possible. To mark an existing image as a shared use the command VBoxManage modifyhd with type shareable.
Something important is that only fixed size disks are supported. If the disk is dynamic you will encounter the following error if you try to modify the image:
ERROR: Cannot change type for medium '/home/vm/ora11g_shared.vdi' to 'Shareable' since it is a dynamic medium storage unit
There is other minor issue, if the image is already attached to two virtual machines the command modifyhd will also fail:
ERROR: Cannot change the type of medium '/home/vm/ora11g_shared.vdi' because it is attached to 2 virtual machines
And finally, YES it works, I have tested it already!
sve@host:~$ VBoxManage showhdinfo /home/vm/ora11g_shared.vdi
Oracle VM VirtualBox Command Line Management Interface Version 3.2.8
(C) 2005-2010 Oracle Corporation
All rights reserved.
UUID: 7521f059-1196-4d68-a1a6-cf0082fb446a Accessible: yes Description: Logical size: 2048 MBytes Current size on disk: 2048 MBytes Type: shareable Storage format: VDI In use by VMs: labs1 (UUID: 25475ff4-70bc-4e2e-aa38-d8fae289273e) labs2 (UUID: e4441f4c-1ef9-42e0-8e54-d2aec2c6cf4f) Location: /home/vm/ora11g_shared.vdi
Regards and happy migration ;)