[rescue] Cheap, fast, PC server
shannon at widomaker.com
Sun Jan 27 12:06:21 CST 2008
On Jan 27, 2008, at 10:24 AM, Lionel Peterson wrote:
>> From: Angel Martin Alganza <ama at ugr.es>
>> Date: 2008/01/27 Sun AM 05:16:18 CST
>> To: The Rescue List <rescue at sunhelp.org>
>> Subject: Re: [rescue] Cheap, fast, PC server
>> On Sat, Jan 26, 2008 at 11:55:39PM -0500, Shannon Hendrix wrote:
>>> My big question in all this is why are people using VMs so much?
>> What about live migration of VMs across different real servers?
>> for upgrades with almost zero downtime. And, of course, the ability
>> to run different operating systems (if that's at all needed) on the
>> same hardware at the same time.
> Personally, I like VMs for building up and tearing down test
> machines very
> quickly -
That's what I use them for, and for that they are nice.
I've also used VMs to get apps moved away from a dying machine
quickly. Move the apps and data, give the VM the old machine's IP,
and you can often get back up and running quickly.
But just for virtualization of app servers and that sort of thing, I'm
not so sure it is a good idea. So far what I see is lower
performance, and what appears to be contention among the stacked
operating systems. It's generally bad for more than one OS to be
managing the same resources, and that's what you get when you use VMs.
Java machines have the same problem to a lesser degree.
VMs are nice in that you can configure one and save it and use it as a
starting point, as long as you don't frequently update your OS.
With jails and zones, it is harder to create pre-configured "zones".
> building, say, a linux server using an Ubuntu ISO file is really
> very quick, much quicker than reading in an actual piece of media.
> In the
> commercial world, a friend's company uses them for setting up test
> environments "on the fly" and for resetting disk images to a known
> state for
> running tests on new code.
I do that too.
However, you need a *LOT* of speed to do this effectively.
I have frequently found I can install a new OS on real hardware and
set up the apps before copying a pre-configured VM finishes.
Even if you use spare virtual disks, VMs get big quickly.
I started out using a NAS on gigabit ethernet to serve images, but
that hasn't worked out too well.
The original idea was to store VMs were any VM server could get to
them, but that's proving very slow.
I could store the VMs on hard drives, but then the other VM servers
can't use them.
I can't afford anything faster than gig ethernet, so I don't have a
ready solution yet.
shannon at widomaker.com
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