We are using Xen 3.0.1 on Debian Sarge from several months. Working great. Finally there is an upgraded manual on HowtoForge – The Perfect Xen 3.0 Setup For Debian . Good. Also something else bring my attention: Setting Up A Highly Available NFS Server . We need this for live migrations – Xen need to get the OS filesystem image from the NFS, but it becoming a single point of failure. Anoter solution can be MogileFS – open source distributed filesystem.
Like a long time shot Parallax (cluster storage system under development by the Xen team with COW and snapshot features) seems pretty atractive.
_Update 28-03-2006: the last missing part from the setup was reliable database backend, found: Load-Balanced MySQL Cluster _
