The Xen Project allows vendors to advertise services and software that use Xen and/or build on top of Xen to advertise their services and/or software in the Xen Project Directory. For more information read the vendor notes.
The Distributed Replicated Block Device (DRBD) is a software-based, shared-nothing, replicated storage solution mirroring the content of block devices (hard disks, partitions, logical volumes etc.) between hosts.
When a DRBD resource is used as a replicated Virtual Block Device (VBD) for Xen, it serves to make the entire contents of a domU's virtual disk available on two servers, which can then be configured for automatic fail-over. That way, DRBD does not only provide redundancy for Linux servers (as in non-virtualized DRBD deployment scenarios), but also for any other operating system that can be virtualized under Xen - which, in essence, includes any operating system available on 32- or 64-bit Intel compatible architectures.