Network Block Device server with support for live migration

 xNBD is a NBD (Network Block Device) server program, which is fully compatible
 with the NBD client driver of Linux kernel. It adds extended features to the
 traditional NBD server:
 .
  * Better performance
  * Support for distributed copy-on-write disks
  * Live storage migration for virtual machines.
  * IPv6 support.
 .
 This is the server side of the program