Here is the complete Xen 4.0 feature list:
- Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per host, 128 physical CPUs per host (as a default, can be compile-time increased to lots more).
- blktap2 for VHD image support, including high-performance snapshots and cloning. Wiki link: blktap2
- Improved IOMMU PCI passthru using hardware accelerated IO virtualization techiques (Intel VT-d and AMD IOMMU). Wiki links: XenPCIpassthrough and VTdHowTo
- VGA primary graphics card passthru support to an HVM guest for high performance graphics using direct access to the graphics card GPU from the guest OS. Wiki links: XenVGAPassthrough
- TMEM allows improved utilization of unused (for example page cache) PV guest memory. more information: http://oss.oracle.com/projects/tmem/
- Memory page sharing and page-to-disc for HVM guests: Copy-on-Write sharing of identical memory pages between VMs.This is an initial implementation and will be improved in upcoming releases.
- New Linux pvops dom0 kernel 2.6.31.x as a default, 2.6.32.x also available. You can also use linux-2.6.18-xen dom0 kernel with Xen 4.0 hypervisor if you want. Wiki link: XenDom0Kernels
- Netchannel2 for improved networking acceleration features and performance, smart NICs, multi-queue support and SR-IOV functionality.
- Online resize of guest disks without reboot/shutdown.
- Remus Fault Tolerance: Live transactional synchronization of VM state between physical servers. run guests synchronized on multiple hosts simultaneously for preventing downtime from hardware failures.
- RAS features: physical cpu/memory hotplug.
- Libxenlight (libxl): a new C library providing higher-level control of Xen that can be shared between various Xen management toolstacks.
- PV-USB: Paravirtual high-performance USB passthru to both PV and HVM guests, supporting USB 2.0 devices. Wiki link: XenUSBPassthrough
- gdbsx: debugger to debug ELF guests
- Support for Citrix WHQL-certified Windows PV drivers, included in XCP (Xen Cloud Platform). Xen Cloud Platform: http://www.xen.org/products/cloudxen.html
- Pygrub improvements: Support for PV guests using GRUB2, Support for guest /boot on ext4 filesystem, Support for bzip2- and lzma-compressed bzImage kernels
- And more..
Thanks again to the Xen.org community for their outstanding efforts in developing this important community release.