[lug] duping minimal vm question

[Michael J. Hammel]

On Thu, 2010-06-03 at 08:57 -0700, karl horlen wrote:
> - what's the best way to install a minimal centos install on a
> "master" client / guest vm?

I found kvm to be a breeze using the virt-manager tools on Fedora.  With
the latter you can use a single command line to do an install from an
ISO of CentOS or any other Linux OS.  I have a bunch of 32 and 64 bit
versions of all the major distros plus some smaller ones.  Installs
occur in a window just like a normal install on your monitor.  It's best
to do this on a system with a big display so the guest install window
fits nicely.

> - once i have that master guest, is it possible to simply use it to
> dup multiple future guests based on teh master?  if so, how easy is
> it?  

The "master" is known as the VM host.  The guest runs on top of that.
Dup'ing guests is known as "cloning".  It's another single command line.
I create base images with the stock distro ISO (without updates) and
then clone those.  The clones use Copy-On-Write so they only update what
they need to.

FWIW I also wrote an init script that pulls config data from a tftp
server so you can reconfigure your guests at boot time based on config
files in the tftp server and the MAC address of the guest.  I just
install it as an RPM or .deb in the base image.  If it doesn't find any
config info, it just skips it.

> - i'm also wondering how many vm guests i can realistically expect to
> rollout on this server before performance suffers?  i know that's
> going to be fairly subjective based on the performance requirements of
> each guest website so guess i'm on my own here.  anybody have a
> formula / method to estimate usage to quantify this before setting up
> the vm guests?

I've run 8 single-core guests with 2GB memory on a quad core host with
8GB total memory with no problem though I won't say they were loaded
guests.  I just verified I could get them running.

No idea how to quantify resource requirements.  You can tweak each
clones config as needed (more memory, more cores, etc.) using the
virt-manager tools.

> fwiw, i imagine each virtualization implementation has it's own
> method[s] so i don't need specifics unless you want to share,
> especially since i haven't picked my vm implementation yet.  but if
> you feel one VM is generally better than another overall or at guest
> vm duping per scenario above, info appreciated.

I've used VMWare and found it much harder to work with than KVM simply
because I can do all the setup and management from the command line with
the virt-manager tools.  Note that the virt-manager tools work with
libvirt and qemu to do their magic.

Hope that helps.
-- 
Michael J. Hammel                                    Principal Software Engineer
mjhammel at graphics-muse.org                           http://graphics-muse.org
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His men would follow him anywhere, ... but only out of morbid curiosity.  
-- From a real employee performance evaluation.