Blog of spblinux

If the same virtual machines should be used on a multi boot system there are at least 3 choices:

• A fat32 partition with virtual disk files. But disk size is limited to 4GB.
• An iSCSI disk connected by network. Speed is limited by network throughput.
• Direct access to hard disk partitions used as virtual disks. With windows a separate hard disk has to be used.

The third choice is described below. Thus a second hard disk only used with virtual machines is required. To allow hard disks with more than 2 TB capacity the disk is partitioned as gpt disk.

Warning: the commands described below can erase the whole data of your hard disks if a mistake is made. Do not continue unless you have a full backup of your system.

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(Yes I am prepared to restore my system in case of a mistake …):

Attach an additional hard disk to your computer which is only used for virtual box images (tested with internal disk; should work with usb disk).
(At least the currently running (host) operating system must not be installed on the same disk).
Add a new partition to the additional hard disk. (If the new virtual disk has 25 GB then the size of the new partion is 25 GB.) In case of a gpt partioned disk up to 128 partitions can be created.

• with a linux host using gdisk the type of the new partition can be set to 0x8301 (linux reserved)
  (internally translated by gdisk to 8DA63339-0007-60C0-C436-083AC8230908)

In case of windows 7 as virtual machine the hardware uuid of the vm must be the same
in the three hosts (linux, osx, windows). (Else the activation of windows 7 cannot be kept.)

•  to display the hardware uuid of the activated vm (with name W7) use:
  VBOxManage showvminfo W7 |grep Hardware
• to set the hardware uuid of a vm (with name W7_1) use the uuid displayed by showvminfo:
  VBoxManage modifyvm W7_1 –hardwareuuid 12345678-1234-abcd-0123-0123456789ab

Using this partition as virtual hard disk with a linux host:

• determine the device name of the new partition, e.g. /dev/sdb7
  (cat /proc/partitions, gdisk -l /dev/sdb …)
• either ad the current user to group disk to allow raw access to all disks
  (has only to be done once; is effective after re-login; but is potentially dangerous).
  Or change the group of /dev/sdb7 to vboxusers
  (to be repeated after reboot)
• run as root user:
  VBoxManage internalcommands createrawvmdk -rawdisk /dev/sdb7 -filename my_filename.vmdk
  and change the ownership of this file to the current user
• run VirtualBox and add my_filename.vmdk as hard disk to the virtual machine

Using this partition as virtual hard disk with a OS X host:

• determine the device name of the new partition, e.g. /dev/disk1s7
  (ls -l /dev/disk* …)
• ad the current user to group operator to allow raw access to all disks
  (is effective after re-login; is potentially dangerous):
  dseditgroup -o edit -a name_of_current_user -t user operator
• Change permission of group from read access to write access
  sudo chmod g+w /dev/disk1s7
  (to be repeated after reboot)
• run as root user:
  VBoxManage internalcommands createrawvmdk -rawdisk /dev/disk1s7 -filename my_filename.vmdk
  and change the ownership of this file to the current user
• run VirtualBox and add my_filename.vmdk as hard disk to the virtual machine
• if OS X auto mounts partitions which should be used by virtualbox: try to deactivate them with disk utility; in case that does not work you can run disk arbitrator which blocks auto mount

Using this partition as virtual hard disk with a Windows 8 64 bit host:

• requires to run VirtualBox with administrative privileges
• determine the device name of the new partition, e.g. diskpart
  list disk
  select disk 1
  list partition
  select partition 7
  detail partition
• windows blocks raw access to the hard disk if the disk is online; use diskpart to switch the disk offline:
  list disk
  select disk 1
  offline disk
• if the disk is mbr partioned open a console window with administrative privileges and run:
  “C:\Program Files\Oracle\VirtualBox\VBoxManage internalcommands createrawvmdk -rawdisk \\.\PhysicalDrive1 -filename my_filename.vmdk -partitions 7
  if the disk is a gpt disk VBoxManage will crash (with VirtualBox 4.2.12) and you have to run this command using a linux host
  VBoxManage internalcommands createrawvmdk -rawdisk /dev/sdb -filename my_filename.vmdk -partitions 7
  (the resulting file my_filename.vmdk hast to be copied to the windows host)
• use wordpad to edit the vmdk file, so that partition 7 is seen as a whole virtual disk:
  (once again a warning: an editing mistake might erase all data of your hard disks)
  change createType to “fullDevice”
  between the lines “# Extent description” and “# The disk Data Base”
  delete all lines except the one refering to partition 7 (e.g. RW 52428800 FLAT “\\.\PhysicalDrive1” 482756608)
  If the vmdk file has been created with linux then the linux device name (e.g. /dev/sdb) has to be replaced
  by the windows device name (e.g. \\.\PhysicalDrive1)
• run VirtualBoxwith administrative privileges and add my_filename.vmdk as hard disk to the virtual machine