Xen

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Revision as of 20:24, 17 December 2009 by Seth (talk | contribs) (Work in progress save for new Xen docs)
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Work in progress. -- Thom 17/12/09

Overview

Creating new Xen instances

Naming your host

  • Think of a name. We like Dr Who themed names! If you recycle a name you'll probably upset Thom -- why not ask Malcolm for advice?
  • At this point you should also create a wiki page explaining your VMs purpose and config. Use one of the other Xen machine's pages as a starting point.
  • Find a free IP and add forward and reverse mappings to the DNS.

Find a Xen host

  • Our main constraints on Xen hosts are RAM and disk space.
  • Use vgs to show free disk space in the volume group
  • Check amount of RAM allocated to dom0 in xentop for a poor estimation of potentially free RAM.

Create disk volumes

  • Create root volume: lvcreate -l 4GB -n <hostname>-root <volume-group>
    • 2GB is just about enough for a Debian install.
    • You can find out the volume group name with vgs
  • Create swap volume: lvcreate -l 256MB -n <hostname>-swap <volume-group>
    • Use your favourite rule of thumb for guessing a completely arbitrary quantity of swap space to allocate. If your machine starts thrashing you'll probably upset someone, so it's better off being small.
  • Create root filesystem: mke2fs -j /dev/<volume-group>/<hostname>-root
  • Create swap filesystem: mkswap /dev/<volume-group>/<hostname>-swap

Create Xen configuration file

Run Debian installer

Booting your instance

xm create -c <newmachinename>.conf

to get the instance up and running. You should be able to log in. Use ctrl+] to get back to the Xen host console.

Booting and Shutting Down

Xen's init scripts are set up to perform an `xm save` (copy the RAM to disk) for each domU that's running when vislor and/or adric are shut down and to restore saved domUs on boot. This should take care of the cases where tardis is shut down intentionally, but a bit more work will have to be done following an unexpected power loss. (When do they happen anyway? ;-)

To start all domUs on vislor do:

for foo in /etc/xen/*.conf; do xm create -c $foo; done
<WAIT FOR A LOGIN PROMPT>
ctrl+]
<WAIT FOR A LOGIN PROMPT>
ctrl+]
....