Seems like Xen is up and down these days. Red Hat is downplaying its Xen connection, thanks to XenSource’s trademark. Linus Torvalds chose KVM over Xen for the Linux kernel. Here are two instances — RHEL5 and the kernel — where a “Xen inside” label would have given Xen some credibility in the corporate market.
In my experience, finding Xen implementations in corporate data centers is as easy as finding penguins in Alaska. Even IT shops that use Linux servers, as most do these days, run VMware and not Xen. IT managers have said to me: Why choose a startup when there’s a free version, VMware Server, that offers more functionality and, of course, maturity? Xen is a virtual nonentity, as far as I can see. If you can prove me wrong with a list of corporate Xen users, I’ll eat an anchovy. Unlike penguins, I hate anchovies.
I just read this short blog entry on kerneltrap.org about why KVM is favored over Xen by some in the open source community:
“Well, there are actually technical reasons in favor of KVM. And kernel developers usually don’t mention them because they are obvious to them. XEN was once designed as a very thin layer underneath the guest OSes. That worked fairly well for the machines XEN was originally used on. But then crazy people came along and wanted to port XEN to other machines, like those 1024CPU altix ones. And they noticed many problems when doing so.
Most of those problems fell into two categories. Either the hardware contained bugs and XEN needed a workaround. In those cases the usual method was to take the workaround from Linux and add it to XEN. Or XEN ran into a scalability problem and was too slow on those machines. In these cases code from Linux was taken, as it already is scalable on all those machines, and added to XEN.
So overall we end up with a formerly thin layer that is accumulating more and more code from Linux as it is getting ported to more and more machines Linux is already running on.”
On the up side, Xen trademark-holder XenSource has introduced a new high-performance line. This offering fills in functionality gaps, like support for Windows guests.
ISV and developer support will be key to XenSource’s success. Xen may not be inside RHEL5 or the kernel, but it could win by being inside virtual appliances.