“During the weekend Xen.org finally released Xen 4.0.

It includes a number of very interesting features, even if they are definitively less than the ones listed in the proposed roadmap appeared in August 2009:

·         Fault Tolerance (live transactional synchronization of VM state between hosts)

·         Memory Overcommit (page sharing through the Transcendent Memory feature)

·         Support for live snapshots and clones through the new VHD implementation called Blktap2

·         Support for new Smart NICs with multi-queue and SR-IOV functionality through the network channel implementation called Netchannel2

·         Support for Para-virtualized USB and VGA pass-through

·         Support for Paravirt-ops in the Dom0 (with Linux kernel 2.6.31)

·         Support for up to 64 vCPUs per virtual machine

·         Support for up to 1TB RAM per host”

http://www.virtualization.info/2010/04/release-xen-40.html