Forum OpenACS Q&A: Solaris Zones vs. Xen vs. Vanilla Debian

See Subject.

I am starting a new OpenACS based project at the hospital I am working at and we are seriously considering going down the OS virtualization route. We have narrowed it down to Xen vs. Solaris Zones. I was wondering if there is any experience with Xen in the community?

I have gotten some initial feedback on Zones from the community (i.e. there is experience using them for OpenACS running PostgreSQL), but we would like to join the Debian install efforts that E-lane has spearheaded and Xen would allow that. As a side note: would also like to avoid trapping ourselves in the quirkiness of Solaris and the joy of installation that quirkiness brings with it).

Any feedback or thoughts are welcome.

Some Links:

• http://www.xensource.com/ is the community site for Xen.
• Xen and the Art of Virtualization (PDF)" is a detailed research paper that describes the Xen hypervisor architecture. This and the other papers on the Xen architecture are invaluable in understanding exactly how Xen works.
• "Xen and the Art of Repeated Research (PDF)" is a performance comparison of XenoLinux (Linux running in a Xen virtual machine) to native Linux as well as to other virtualization tools on an IBM eServer™ zSeries® mainframe. It repeats an earlier performance analysis for consistency of results.
• "Virtualization and the On Demand Business" (IBM Redpaper, August 2004) describes how organizations can use virtualization as a technique to gain more business value and greater flexibility from their IT infrastructure.

I think Cathy is using User Mode Linux. I have ruled out UML based on research and problems getting a testing environment up.

Getting a test version of Xen running was simple ( http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads.html ). In fact I had the Xen Demo up and running before I finished reading through the license and downloading the second Solaris 10 CD from Sun (iirc there where ~6).

http://lists.xensource.com/archives/html/xen-devel/2005-02/msg00868.html

I like these two:

- move running virtual machines to another host without stopping them

- pickle a virtual machine's state to disk and resume it later (wonder if the paused server can be moved easily to another machine as well)

On the Vserver site I found this wish from Cathy:

"Biggest wish: more resource allocation abilities, especially for memory."

http://linux-vserver.org/VServer+Hosting

Is that still the case Cathy? This is one of the positive things I read about Solaris Zones (nice allocation between zones... e.g. if one zone needs RAM and anothers are not using it all, that machine can take adavantage of the situation). Wondering how Xen deals with this.

Also, here is a Xen limitation that could be important for heavy trafficked sites: "Xen can currently use up to 4GB of memory. It is possible for x86 machines to address up to 64GB of physical memory but there are no current plans to support these systems: The x86/64 port is the planned route to supporting larger memory sizes." How much RAM does a site like Galileo typically need? On the other hand, we do have a load balancer for clinical applications and could possibly use it to distribute load to various Xen instances on different physical boxes.

Depending on your requirements this can be a good thing or a bad thing. Do you actually need to run several different OSs or OS versions on your production servers? If not then virtualisation along the Zones/Jail line is actually a win since you don't have the resource hit (memory mainly, but also cycles) of running multiple kernel images at the same time.