Matt Mossholder on 21 Jun 2008 15:52:52 -0700

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Re: [PLUG] Why Virtualize?

----- "Casey Bralla" <> wrote:
> But why not simply run dozens (hundreds?) of server **instances** on
> the same 
> server?   Why add the extra overhead of the virtualization process to
> the 
> hardware?   That has to cut efficiency by at least a few percent.
> So what is the advantage of running a complete virtualized server
> instead of 
> multiple server processes?  I can think on only 1:  Clearly assignable

I am in total agreement with you here. Consolidating applications to a single server is a good thing. However, the factor that many people forget to take into account is the additional cost savings that could be had by consolidating software licensing as well. At my employer, someone came up with the brilliant idea of using VMWare ESX to put a single server at our smaller offices, to run all of the apps they use. Unfortunately, these apps amount to:

   * DHCP
   * DNS
   * File Server
   * Print Server
   * Site specific web server

So, they decided to allocate a VM to each function. Of course, to remain within our company standards, each of these VMs also needed to run:

   * BMC Patrol (problem monitoring)
   * Anti-virus software
   * Asset Management software
   * Centralized remote access software
   * Systems Management software

All of these coses could have been reduced by 4/5ths if all of these trivial applications were run on a single OS. None of them are particularly complex, or likely to interfere with each other. That's not even including the costs to purchase and maintain ESX and the price of keeping all the additional OSs.

> responsibility for operation.    (If I am responsible for apache on a
> server, 
> and you are responsible for sendmail, I'll try to blame you when I
> screw up 
> and apache stops working.)  Virtualization also is good where someone
> is 
> selling customer-maintained server time in a server farm.  (Again, to
> isolate 
> human responsibility, not to isolate program execution, per se.)
> But other than this specific case, what the heck is the advantage?
> -- 
> Casey Bralla
> Chief Nerd in Residence
> The NerdWorld Organisation

Another advantage is political. It is often easier to get people to migrate to a VM (which can be done with tools) than to get them to reinstall their software on a new system, configure it, move the data, and point all the clients to the new system.

Another advantage on the energy front comes from migrating running VMs between systems. VMWare calls it VMotion, Xen has Live Migration, etc.  I know with VMotion, you can do things like migrate a bunch of running VMs to a smaller number of servers at night, when load is low, and shutdown the excess systems, and then move them back out in the morning as load increases.

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