With the recent acquisition of XenSource by Citrix, it seems like a good idea to take a look at the history of Xen and XenSource so we have our bearings once the dust settles. This will be a brief look, but I'm sure more details will come out from you "Xen Experts" in the comments.
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First off, XenSource is a commercial company that sells a suite of enhancements and management products that augment an open-source hypervisor called Xen. The lead developer for XenSource, Ian Pratt, is also the chief architect of the Xen open-source project - a competitive leg up by no small means. In fact, XenSource is the key corporation behind the Xen hypervisor, so any enhancements to Xen also enhance XenSource (and anyone else who uses Xen, for that matter).
XenSource's goal, to put it unofficially, is to provide a solution akin to VMware, but using an open-source hypervisor. This hypervisor has differences from VMware that some call advantages. Some also call them disadvantages, which has led to what appears to be an epic battle akin to NT/Novell circa 1996. More on this battle in future articles, I'm sure. XenSource originally started as a pay-for support option for organizations that wanted to run the Xen hypervisor. Over the last few years, they have created an impressive suite of management solutions for Xen, and have even collaborated with Microsoft.
Xen, first released to the public in 2003, uses a type of virtualization called "paravirtualization." This is essentially a software method of interfacing virtual machines to the host hardware...sort of an API. Because of this, Linux operating systems have to have modifications made to run as a guest on a Xen server (called "Xen-enabled"). This is the part that sparked that battle between the VMware guys and the Xen guys. VMware uses a method called Binary Translation, which uses hidden hardware instructions to accomplish the same thing (that is, functional virtual machines).
With the advent of Intel VT and AMD SVM, Xen now supports Windows virtual machines without changes to the guest OS (Windows virtual machines were not supported prior to support for VT and SVM). This has brought the virtualization methods of the two companies a little closer together, but still fundamentally different.
Note: I tried really hard to get that right, but if I missed something or am way off base, please email me and let me know the real deal.
From 2003 to 2005, Xen's relative youth, it was developed into a popular desktop hypervisor. Able to support only one 32-bit processor, there wasn't much enterprise appeal. This is when XenSource was simply a commercial Xen support company. In 2005, XenSource released Xen v3, the first enterprise-class release of Xen (even though it was called version 3, it was really the first). With this release Xen could run on servers with up to 32 processors, and was the first version with built-in support for Intel's VT technology. AMD hadn't released SVM yet, but it too was eventually supported. In addition to the processor enhancements, Xen v3 also introduced support for Physical Address Extensions (PAE) to support 32-bit host servers with more than 4GB of memory. At this point, Xen still only supported Xen-enabled Linux guest operating systems.
The v3 release of Xen also resulted in XenSource's first legitimate approach to an enterprise solution - XenOptimizer. XenOptimizer was intended to be bridge the gap between Xen and VMware. Remember, Xen is just the hypervisor, XenOptimizer from XenSource (confusing, eh?) was the management interface. With XenOptimizer, admins were now able to manage multiple servers from a common interface for server provisioning and resource control.
In late 2006, XenSource released its first version of XenEnterprise 3.0, a product meant to directly compete with VMware. Based on v3.03 of Xen, it included an new management and monitoring console built on XenOptimizer and, most importantly, support for Windows guest operating systems. This is largely the result of a July 2006 partnership agreement between XenSource and Microsoft to provide interoperability between XenSource and Microsoft's new hypervisor, codename Viridian. Also resulting from this agreement, Xen-enabled Linux guests will be able to run on Viridian and XenEnterprise will be able to recognize Viridian's VHD (Virtual Hard Drive) files.
Flash forward to just over a week ago, when XenSource released XenEnterprise v4. This is a landmark release for XenSource, and builds on the foundation laid by XenEnterprise v3. The new version adds features and functionality that are meant to rival VMware, but at less than half the cost (list price, of course). Among the new features are:
- Integrated storage management software, Veritas Storage Foundation from Symantec
- XenMotion, the Xen equivalent to VMware's VMotion
- A new system management console, XenCenter, allowing administrators to manage virtual machines just as a user would do with VMware VirtualCenter.
XenEnterprise v4 runs on the latest version of Xen, v3.1 (sigh...Citrix, please change XenSource's name to something else...like Tazwell or Oddibe).
That brings us up to the present day. It’s been a busy (and profitable) last few weeks for XenSource, and Citrix is so light in the pocketbook now that they’ve had to tie themselves down with all the red tape they’ve gotten stuck in by purchasing the sponsor company of an open-sourced hypervisor. It’s in Citrix’s best interest to continue to develop Xen, since any improvements will undoubtedly help them. The crazy thing is that those same improvements will now also help out their new direct competitor – VirtualIron.
Some quick thoughts about the future…
As the dust has settled over the past few days and I’ve had a chance to look at the reactions of many people, both analysts and admins, it’s pretty clear that the nobody knows for sure what is going to come of all this. There are obvious correlations between XenEnterprise and Citrix Desktop Server, and Citrix may even be able to use some of the Xen technology to enhance AIE and Citrix Streaming server. So far, the most interesting thing I’ve heard comes from a guest’s post in our forums. An excerpt from that post reads:
“It seems to me that Citrix is looking to strike the same deal with Microsoft regarding virtualization that it has regarding Terminal Services: Microsoft provides the underlying infrastructure and Citrix provides the enterprise solution on top of it. If this is true, then this purchase was probably done with Microsoft’s blessing, and positions Microsoft and Citrix as partners against VMware.”
If that is indeed the case, then the next year or so could be pretty cool in a UFC/Rugby/Australian Rules Football kind of way.