Xen zen? Anyone?
debian at herakles.homelinux.org
Fri Nov 25 21:57:45 UTC 2005
David Cary Hart wrote:
> On Fri, 2005-11-25 at 13:25 -0500, Matt Morgan wrote:
>>On 11/25/05, David Cary Hart <Fedora at tqmcube.com> wrote:
>>>This is an exercise in intellectual curiosity. Do I understand the
>>>I see two possible applications:
>>> 1) Running instances of FC4 and FC5 beta as virtual machines.
>>> Does this make sense?
>>> 2) Splitting a server into functional virtual machines. For
>>> example, an instance running postfix, an instance running httpd
>>> and an instance for rbldnsd.
>>> a) Does this improve performance?
>>> b) Is it safe on a production server?
>>All your examples are possible.
>>I don't think Xen improves performance in any way. It causes less of a
>>hit than User-Mode Linux, however.
Think of a small hosting concern. My mate runs three servers, one for
mail, one for web, one for other stuff.
Think one real server, one UPS (or a smaller one, or it lives longer),
one CPU etc,
> Crenshaw said the drive toward virtualization has been further
> invigorated by data that shows the average server uses between
> 15% and 25% of its CPU capacity. Virtualization, on the other
> hand, could improve that to 80% or more, "so you can get more
> productivity from less hardware," he said, adding that "it comes
> down to more productivity at less cost. [You can] take advantage
> of faster, better, cheaper hardware more quickly and without
> extensive qualification cycles because the software is qualified
> to the virtual machine rather than the hardware."
I don't think you'd want to go beyond 80% because if you do
responsiveness will suffer. Even at 80% you'd want to think about an
Speaking of which, xen offers the ability to upgrade with zero downtime:
if my mate set it up properly and he found spamassassin in the
mailserver holding up the web server, he could bring a real server out
of retirement and move the running mail (or web) server onto it.
Read the docs, it's really cool stuff. And, unlike UML, it actually
seems to be an active project. Each time I checked out UML and the past
couple of years I couldn't tell anything useful was happening.
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