Xen supports two Virtual Block Device types natively:
phy
. This device type is used to hand "physical" block devices, available
in the host environment, off to a guest domU in an essentially
transparent fashion.
file
. This device type is used to make file-based block device images
available to the guest domU. It works by creating a loop block device
from the original image file, and then handing that block device off
to the domU in much the same fashion as the phy
device type does.
If a Virtual Block Device configured in the disk
option of a domU
configuration uses any prefix other than phy:
, file:
, or no prefix
at all (in which case Xen defaults to using the phy
device type),
Xen expects to find a helper script named block
-prefix in the Xen
scripts directory, commonly /etc/xen/scripts
.
The DRBD distribution provides such a script for the drbd
device
type, named /etc/xen/scripts/block-drbd
. This script handles the
necessary DRBD resource state transitions as described earlier in this
chapter.