Citrix resurrects King George as hypervisor

As it preps the next release of its XenServer virtual machine hypervisor, Citrix is reliving the American Revolution.

The company's XenServer dev team - on the move from Britain to Boston - is putting the finishing touches on a new version code-name "George," after King George III. And the next release is dubbed "Midnight Ride," after Paul Revere's famous gallop.

The core open-source Xen project is still anchored at Cambridge University under Ian Pratt - founder of the project and vice president of advanced product for Citrix' Virtualization and Management Division - but the commercialized product, XenServer, has its own team. It's this team - heavy into management tools for virtual server environments - that's moving to Boston from the United Kingdom.

Citrix already had a team in Boston dedicated to its Provisioning Server (which was merged into the XenServer stack after Citrix shelled out $500m to buy XenSource, the company behind Xen, in the summer of 2007). Another Citrix acquisition, Reflectent Software, which created an access and systems management tool called EdgeSight, is also located in Boston.

The United States is still the largest IT market, and Boston is place where the working day overlaps with both business hours in both Europe and California. The same goes for Fort Lauderdale, Florida, where Citrix has its headquarters.

According to Simon Crosby - the chief technology officer at Citrix' Virtualization and Management Division - the XenServer development team is amusing itself with code names. After "George" and "Midnight Ride," it will deliver "Boston." In the early years, Crosby says, XenSource could do a dot release on its commercial products every six months or so, but going forward, Citrix expects to take about nine months to get each new release into the field.

"It's not so much the rate the Xen engineers can get changes done," explains Crosby, "but how quickly you can get the changes absorbed by the channel. You have to train everybody in how to use and sell these features."

Welcome to enterprise computing. Not as much fun as free-wheeling open source, eh? But the pay is probably bigger and steadier. And the install base grows faster, too. Xen was on fewer than 10,000 machines when Citrix acquired the company in August 2007, and by the time XenServer 5.0 was launched last September, that number had grown to 250,000 production servers using XenServer.

Last summer, Citrix estimated that as much as one-fifth of the servers that have been virtualized to date had one or another flavor of Xen on them. (Citrix, Oracle, and Sun sell commercialized versions of Xen, while Red Hat and Novell embed a Xen hypervisor inside their commercial Linuxes. There is some confusion as to whether or not Sun has actually shipped its xVM Server variant of Xen).

Crosby says that George (XenServer 5.1) will come out sometime in the first quarter of this year. That means Midnight Ride (5.2) will arrive between late 2009 to early 2010 and Boston (5.3) will debut at the end of 2010.

XenServer 5.0, launched last September, is based on the Xen 3.2 hypervisor with a couple of extra patches slapped on it by Citrix to deal with BIOS and firmware security issues on x64 platforms. XenServer 5.1 will be based on the Xen 3.3 hypervisor, which has been optimized for Intel's forthcoming "Nehalem" Xeon server chips and, presumably also for Advanced Micro Device's current "Shanghai" Opterons. Both of these processors have lots of electronic support for virtual machine hypervisors.

Xen 3.3 can be used to virtualize x64, Itanium, and ARM processors, but the commercial XenServer product sold by Citrix only runs on x64 iron. Xen 3.3 has features that allow for dynamic reallocation memory between guest VMs and for VMs to migrate between different generations of processors. Xen 3.3 also includes support for power management features on servers, which can gear down or shut down unused components (such as cores and caches) that are not being used by workloads.

To whet the appetites a bit, Crosby gave a few hints about what is coming up in the XenServer 5.1. First, he says that the company will be making "substantial enhancements" to the high-end Platinum Edition of XenServer, but then he laughed and wouldn't say what these enhancements might be.

Crosby did say that Citrix is taking the EdgeSight product it acquired last year and is transforming it into a distributed workload management tool for XenServer hypervisors and their VMs, akin to VMware's distributed resource scheduler (DRS) add-on to its VirtualCenter management tool. The question here is whether either tool will be able to manage the virtual machines hosted on the other's hypervisors. VMware's DRS only works on ESX Server hypervisors, so there is an opportunity for Citrix to go broad once it gets the feature out the door for XenServer.

Another interesting and much-needed feature will allow so-called stub I/O domains to be set up on a physical server so that access to multiple driver stacks for the devices attached to that server can be multiplexed. Boosting bandwidth, this will cope with I/O bottlenecks in virtualized environments.

The way Xen works today, domain 0, or the host or privileged domain in the Xen architecture, is where device drivers run, and all VMs have to talk to domain 0 for their I/O. With stub domains, a lot of the I/O functionality of domain 0 is replicated and does not run with root access to domain 0, which nonetheless still has privileged access to the hardware. This I/O multiplexing capability is an outgrowth of the passthrough support that Intel cooked into the VT-d electronics in its most current x64 chips. Passthrough allows a physical device to be tied to a specific VM to boost its performance. ®