Release: Xen 4.0 – UPDATED

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During the weekend 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
  • Support for Intel Xeon 5600 Series CPUs (codename Westmere)

One significant omission is the integration with Open vSwitch, which launched in August 2009.
The thing is particularly strange considering that the distributed virtual switch is part of the Xen Cloud Platform (XCP), which is based on Xen.
Maybe the product is not yet solid enough, or it doesn’t have enough features, to be included in a mature release of Xen like this one.

Now, it’s just a matter to see how quickly the new engine will be implemented in XCP, Citrix XenServer, Novell SLES and Oracle VM Server, and what kind of additional features these companies will be able to build on top of Xen 4.0.

Update: and Citrix reached out to clarify some points about this release, so is able to correct some statements above and add additional information about Xen 4.0.

First: the approach has is to continue developing Xen as just a virtualization engine. Anything on top of it and around it should follow its own development. This is why including Open vSwitch in Xen doesn’t really make sense, while bundling it in XCP is more appropriated.

Second: the new features that Xen 4.0 offers will shortly appear in both XCP and Xen Hypervisor for Client Devices (XCI). They should appear in a couple of months or so.
Some of these features then will make their way into Citrix XenServer (which derives from XCP) and the upcoming Citrix XenClient (which derives from XCI). In the case of XenServer, the selected features may not appear before six months.

Third: the VGA pass-through capability is supported by some NVIDIA, ATI and Intel graphic cards, even if there’s not yet a specific list yet that users can check.

Fourth: at the moment doesn’t to release any benchmark about Xen 4.0 (compared for example to Xen 3.x or other hypervisors) but such performance analysis may appear at the upcoming Xen Summit.