Xen versus VirtualBox

Xen versus VirtualBox

Posted Aug 12, 2008 17:17 UTC (Tue) by leighbb (subscriber, #1205)
Parent article: Sun's FOSS VirtualBox hits the sweet spot for Linux (ITWire)

VirtualBox is a beautiful product - easy to use and pretty to look at. The downside is that it is very slow. I'd go as far as to say unusable for server virtualisation. I have six stripped-down Debian installations running on my machine and they are EACH taking around 6% of a CPU, while being pretty idle. This is on a dual-core Dell SC440 :-

leigh@scales:~$ ps -o "pid ppid pcpu comm" -u leigh | grep VirtualBox
 6007     1  0.0 VirtualBox
 6034  6024  6.0 VirtualBox
 6054  6024  6.1 VirtualBox
 6076  6024  5.9 VirtualBox
 6096  6024  6.0 VirtualBox
 6116  6024  6.1 VirtualBox
 6135  6024  6.0 VirtualBox

On the other hand I have an old P4 2.4GHz running Xen with 7 guests, that are in production (though that not busy), and the overhead is minimal. I use Debian so getting a domain up and running is relatively straight forward.

xentop - 18:09:05   Xen 3.0.2-2
7 domains: 1 running, 4 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown
Mem: 2095680k total, 1575500k used, 520180k free    CPUs: 1 @ 2411MHz
      NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)
  domain04 ------      66044    1.9     393012   18.8
  Domain-0 -----r      17301    0.6     106648    5.1
  domain03 --b---      18649    0.6     130896    6.2
  domain07 --b---      20127    0.6     393064   18.8
  domain08 --b---      11386    0.2     130880    6.2
  domain33 ------      81066    0.3     261888   12.5
  domain10 --b---       3832    0.8     130828    6.2

NB: I've tweaked the output from xentop command to change the names of the domains and remove some of the columns.

Para-virtualisation is worth the pain, in my book, but its definitely horses for courses.

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On CentOS we have also seen comparable idle guest load. Setting the timer frequency
(CONFIG_HZ) to a lower value will often help much. Of course, it's up to you to decide if
that's ok for your workload.

There's more information here:
http://bugs.centos.org/view.php?id=2189

If you are doing a lot of Linux on Linux virtualization, check out the two OS Virtualization
systems available for Linux: 1) OpenVZ and 2) Linux-VServer.  Both are good but my personal
preference is OpenVZ.

Xen and KVM work well... but... OS Virtualization is much lighter and more efficient than
machine / hardware virtualization and provides much greater density and scalability.  The
large number of dynamic resource management parameters offered by OS Virtualization are a big
bonus too.