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I don't care about GUI or tools, but I do care about stability and performance. If I'm running a FreeBSD firewall and a Opensolaris file server as guests, will I get better stability or performance (network and disk i/o) if I switch to KVM? Follow-up question: which is most likely to be rock-stable and near-native i/o speeds in the future?

More details:

Currently I have a xen server with an OpenSuse dom0 and several domUs including *NIX and *BSD.

Problems I currently have with the latest xen as of ~August:

  • Networking in PV kernels buggy: can't change MAC of vif in dom0, packets get lost if using a domU as a firewall
  • FreeBSD 8.1 not stable as a PV domU
  • HVM domUs not stable under heavy I/O load

Supposedly the networking bug in the PV kernels is fixed, so I'm looking to switch distros to one that uses pv kernels. I figured that if I'm going to redo Xen from scratch, might as well look at the competition and KVM seems somewhat promising.

EDIT: I don't care about GUI/management tools as I only use command-line options.

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KVM is now in the Linux kernel, and as of late seems to have more momentum -- e.g, Red Hat has switched to supporting it over Xen. That said, I don't see Xen going away anytime soon, and if you feel more comfortable with Xen you're probably fine with it, especially since they share many of the same managment tools through libvirt. Both will also get pretty good performance through virtio, and though my experience is with KVM, I'd consider them both "rock solid" for a wide variety of guests/domUs.

Edit: I should add that we've run a huge variety of guests under KVM, including FreeBSD firewalls, with none of the issues you've mentioned -- it has just worked.

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  • You ran FreeBSD 8.0/8.1 under KVM with PV drivers? Was searching and thought FreeBSD didn't have PV KVM drivers.
    – user57766
    Oct 21, 2010 at 5:59
  • to be fair, ive never had those issues with xen, either.
    – Sirex
    Oct 21, 2010 at 7:28
  • You are correct, I should have made that clearer in my edit -- for FreeBSD guests in particular, we use e1000 rather than virtio, since FreeBSD doesn't do kernel caching/block devices. However, this is true for both KVM and Xen.
    – nedm
    Oct 21, 2010 at 17:22
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In addition/support of what has already been identified. Another possible consideration is that Xen has the backing of Citrix and is also a large technology base behind Microsoft's Hyper-V. Those two can be significant factors to consider...

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