On 2 Jul 2014, at 4:19 pm, Jonathan Aquilina <jaquil...@eagleeyet.net> wrote:

> How would the same arguments apply if you are just dealing with dns
> servers web servers databases etc.

If you're just dealing with standard services then you're not really doing high 
performance clustering, but fault tolerance.

In a typical enterprise data centre you're also more likely to have one server 
per application, or just a small handful of applications, and so you can 
configure each server appropriately.

In our environment we're specifically dealing with the case that not only are 
we running a handful of commercial packages, but also a lot of in house home 
grown code, often bought in from research centres around the world. They're 
written by many different people with access to a lot of different software and 
hardware, and we do our best to accommodate them all, all at once, in a single 
shared application space.

Beyond that, researchers also have to shoot for reproducibility. If they 
produce a set of results, then they should, and often do, release the exact 
details of the environment under which their results were obtained. This way if 
someone else gets different results to their research, using the same set of 
inputs, they can go back and rerun their simulations under the same code 
versions as last time, and compare to try and eliminate the possibility that 
their results were fraudulently generated (ie, they faked their research), they 
may have just been running on a buggy version of software.

Enterprises do often keep older versions of compilers and Operating Systems 
around for reasons of backwards compatibility. When Windows Vista came out, a 
Dev I was working with at the time, insisted on upgrading to Vista and the 
latest version of Visual Studio, despite his customer still being on XP. He 
later downgraded everything back to XP when he found he couldn't compile the 
clients application anymore, and his versions wouldn't work on their XP systems.

Compilers change, CPUs change, operating systems change, applications change, 
usually at different rates, and frequently in separate directions. How much you 
need to support all at once will be a big factor in how you go about setting up 
your environment.
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