Friday, March 28, 2008

True myths

The appearance of kvm naturally provoked reactions from the competition, which are interesting in the way they imply some untruths while being 100% accurate:

  • kvm is good for desktop -- that is eminently true, by being integrated with Linux kvm inherits all the desktop and laptop goodies, like excellent power management, suspend/resume, good regular (non-virtual-machine) process performance, and driver integration.

    The implication, however, is that kvm is not suitable for server use. This is wrong: kvm also inherits from Linux its server qualities, including excellent scalability, advanced memory management, security, and I/O stack.

  • you need a bare metal hypervisor for server workloads -- that is also true, without complete control of the hardware a hypervisor will be hopelessly inefficient.

    Somehow the people who say this ignore the fact that kvm is a bare metal hypervisor, accessing the hardware directly. In fact kvm is much closer to the bare metal than Xen, which can only access I/O devices through a special guest, "dom0", which is definitely not running on bare metal.

  • A thin hypervisor gives better security -- true again, the smaller your trusted computing base is, the greater confidence you have in your hypervisor.

    The same speakers then go on about how thin Xen is. But they seem to ignore that the entire I/O and management plane is in fact a Linux guest -- and that it is part of the trusted computing base. Now which is smaller, Linux, or Xen with a trusted Linux guest?

Developers, of course, realize all of this immediately; but it will take some time and counter-marketing to repair the damage already done. Hence this article.