2.8. Advanced Storage Configuration

2.8.1. Using a Raw Host Hard Disk From a Guest

As an alternative to using virtual disk images as described in Virtual Storage, Oracle VM VirtualBox can also present either entire physical hard disks or selected partitions as virtual disks to virtual machines.

With Oracle VM VirtualBox, this type of access is called raw hard disk access. It enables a guest operating system to access its virtual hard disk without going through the host OS file system. The actual performance difference for image files compared to raw disk varies greatly depending on the overhead of the host file system, whether dynamically growing images are used, and on host OS caching strategies. The caching indirectly also affects other aspects such as failure behavior. For example, whether the virtual disk contains all data written before a host OS crash. Consult your host OS documentation for details on this.

Warning

Raw hard disk access is for expert users only. Incorrect use or use of an outdated configuration can lead to total loss of data on the physical disk. Most importantly, do not attempt to boot the partition with the currently running host operating system in a guest. This will lead to severe data corruption.

Raw hard disk access, both for entire disks and individual partitions, is implemented as part of the VMDK image format support. As a result, you will need to create a special VMDK image file which defines where the data will be stored. After creating such a special VMDK image, you can use it like a regular virtual disk image. For example, you can use the VirtualBox Manager, see The Virtual Media Manager, or VBoxManage to assign the image to a virtual machine.

2.8.1.1. Access to Entire Physical Hard Disk

While this variant is the simplest to set up, you must be aware that this will give a guest operating system direct and full access to an entire physical disk. If your host operating system is also booted from this disk, please take special care to not access the partition from the guest at all. On the positive side, the physical disk can be repartitioned in arbitrary ways without having to recreate the image file that gives access to the raw disk.

On a Linux host, to create an image that represents an entire physical hard disk which will not contain any actual data, as this will all be stored on the physical disk, use the following command:

VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk
  -rawdisk /dev/sda

This creates the image /path/to/file.vmdk, which must be an absolute path. All data will be read and written from /dev/sda.

On a Windows host, instead of the above device specification, for example use \\.\PhysicalDrive0. On a Mac OS X host, instead of the above device specification use for example /dev/disk1. Note that on Mac OS X you can only get access to an entire disk if no volume is mounted from it.

Creating the image requires read/write access for the given device. Read/write access is also later needed when using the image from a virtual machine. On some host platforms, such as Windows Vista and later, raw disk access may be restricted and not permitted by the host OS in some situations.

Just like with regular disk images, this does not automatically attach the newly created image to a virtual machine. This can be done as follows:

VBoxManage storageattach WindowsXP --storagectl "IDE Controller"
 --port 0 --device 0 --type hdd --medium /path/to/file.vmdk

When this is done the selected virtual machine will boot from the specified physical disk.

2.8.1.2. Access to Individual Physical Hard Disk Partitions

This raw partition support is quite similar to the full hard disk access described above. However, in this case, any partitioning information will be stored inside the VMDK image. This means that you can install a different boot loader in the virtual hard disk without affecting the host's partitioning information. While the guest will be able to see all partitions that exist on the physical disk, access will be filtered in that reading from partitions for which no access is allowed the partitions will only yield zeroes, and all writes to them are ignored.

To create a special image for raw partition support, which will contain a small amount of data, on a Linux host, use the command:

VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk
 -rawdisk /dev/sda -partitions 1,5

The command is identical to the one for full hard disk access, except for the additional -partitions parameter. This example would create the image /path/to/file.vmdk, which must be absolute, and partitions 1 and 5 of /dev/sda would be made accessible to the guest.

Oracle VM VirtualBox uses the same partition numbering as your Linux host. As a result, the numbers given in the above example would refer to the first primary partition and the first logical drive in the extended partition, respectively.

On a Windows host, instead of the above device specification, use for example \\.\PhysicalDrive0. On a Mac OS X host, instead of the above device specification use /dev/disk1, for example. Note that on OS X you can only use partitions which are not mounted. Eject the respective volume first. Partition numbers are the same on Linux, Windows, and Mac OS X hosts.

The numbers for the list of partitions can be taken from the output of the following command:

VBoxManage internalcommands listpartitions -rawdisk /dev/sda

The output lists the partition types and sizes to give the user enough information to identify the partitions necessary for the guest.

Images which give access to individual partitions are specific to a particular host disk setup. You cannot transfer these images to another host. Also, whenever the host partitioning changes, the image must be recreated.

Creating the image requires read/write access for the given device. Read/write access is also later needed when using the image from a virtual machine. If this is not feasible, there is a special variant for raw partition access, currently only available on Linux hosts, that avoids having to give the current user access to the entire disk. To set up such an image, use:

VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk
 -rawdisk /dev/sda -partitions 1,5 -relative

When used from a virtual machine, the image will then refer not to the entire disk, but only to the individual partitions. In this example, /dev/sda1 and /dev/sda5. As a consequence, read/write access is only required for the affected partitions, not for the entire disk. During creation however, read-only access to the entire disk is required to obtain the partitioning information.

In some configurations it may be necessary to change the MBR code of the created image. For example, to replace the Linux boot loader that is used on the host by another boot loader. This enables for example the guest to boot directly to Windows, while the host boots Linux from the "same" disk. For this purpose the -mbr parameter is provided. It specifies a file name from which to take the MBR code. The partition table is not modified at all, so a MBR file from a system with totally different partitioning can be used. An example of this is:

VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk
 -rawdisk /dev/sda -partitions 1,5 -mbr winxp.mbr

The modified MBR will be stored inside the image, not on the host disk.

The created image can be attached to a storage controller in a VM configuration as usual.

2.8.2. Configuring the Hard Disk Vendor Product Data (VPD)

Oracle VM VirtualBox reports vendor product data for its virtual hard disks which consist of hard disk serial number, firmware revision and model number. These can be changed using the following commands:

VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/SerialNumber" "serial"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/FirmwareRevision" "firmware"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/ModelNumber" "model"

The serial number is a 20 byte alphanumeric string, the firmware revision an 8 byte alphanumeric string and the model number a 40 byte alphanumeric string. Instead of Port0, referring to the first port, specify the desired SATA hard disk port.

The above commands apply to virtual machines with an AHCI (SATA) controller. The commands for virtual machines with an IDE controller are:

VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/piix3ide/0/Config/PrimaryMaster/SerialNumber" "serial"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/piix3ide/0/Config/PrimaryMaster/FirmwareRevision" "firmware"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/piix3ide/0/Config/PrimaryMaster/ModelNumber" "model"

For hard disks it is also possible to mark the drive as having a non-rotational medium with:

VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/NonRotational" "1"

Additional three parameters are needed for CD/DVD drives to report the vendor product data:

VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/ATAPIVendorId" "vendor"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/ATAPIProductId" "product"
VBoxManage setextradata "VM name"
      "VBoxInternal/Devices/ahci/0/Config/Port0/ATAPIRevision" "revision"

The vendor id is an 8 byte alphanumeric string, the product id an 16 byte alphanumeric string and the revision a 4 byte alphanumeric string. Instead of Port0, referring to the first port, specify the desired SATA hard disk port.

2.8.3. Access iSCSI Targets Using Internal Networking

As an experimental feature, Oracle VM VirtualBox enables access to an iSCSI target running in a virtual machine which is configured to use Internal Networking mode. See iSCSI Servers, Internal Networking, and VBoxManage storageattach.

The IP stack accessing Internal Networking must be configured in the virtual machine which accesses the iSCSI target. A free static IP and a MAC address not used by other virtual machines must be chosen. In the example below, adapt the name of the virtual machine, the MAC address, the IP configuration, and the Internal Networking name (MyIntNet) according to your needs. The following eight commands must first be issued:

VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/Trusted 1
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/Config/MAC 08:00:27:01:02:0f
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/Config/IP 10.0.9.1
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/Config/Netmask 255.255.255.0
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/LUN#0/Driver IntNet
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/LUN#0/Config/Network MyIntNet
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/LUN#0/Config/TrunkType 2
VBoxManage setextradata "VM name" VBoxInternal/Devices/IntNetIP/0/LUN#0/Config/IsService 1

Finally the iSCSI disk must be attached with the --intnet option to tell the iSCSI initiator to use internal networking, as follows:

VBoxManage storageattach ... --medium iscsi
--server 10.0.9.30 --target iqn.2008-12.com.sun:sampletarget --intnet

Compared to a regular iSCSI setup, the IP address of the target must be specified as a numeric IP address, as there is no DNS resolver for internal networking.

The virtual machine with the iSCSI target should be started before the VM using it is powered on. If a virtual machine using an iSCSI disk is started without having the iSCSI target powered up, it can take up to 200 seconds to detect this situation. The VM will fail to power up.