[Beowulf] RE: Capitalization Rates - How often should you replace a cluster? (resent - 1st sending wasn't posted ).
eagles051387 at gmail.com
Mon Jan 19 23:14:35 PST 2009
in all honesty is there a need really to replace the cluster. why not just
add onto it?
On Mon, Jan 19, 2009 at 2:40 AM, Robert G. Brown <rgb at phy.duke.edu> wrote:
> On Sun, 18 Jan 2009, Greg Lindahl wrote:
> On Fri, Jan 16, 2009 at 08:10:43PM -0500, Mark Hahn wrote:
>>> The question was raised as "When should all these servers be upgraded or
>>>> replaced again?"
>>> 3-5 years, IMO. if you replace hardware in <3 years, you're obviously
>>> burning money.
>> After factoring in rent and utilities, my replacement time is < 3
>> years. So what's obvious to you doesn't seem very obvious to me!
> Right. There are rules of thumb, but they are based on assumptions, and
> if the assumptions aren't applicable they will lead to non-optimal
> behavior. The right rule is "do the cost-benefit analysis and act
> according to what it tells you". Which will, in fact, often lead to 3-5
> year replacement cycle. But additional costs along the way alter the
> landscape, shifting to different replacement cycles.
> To do the computation correctly, you have to include all sorts of
> marginal costs and benefits. For example, sometimes there are nonlinear
> benefits to finishing work faster, which favors shorter cycles.
> Sometimes there are nonlinear costs (or higher than normal linear
> costs, which ALSO favors shorter cycles.
> On the other hand, if somebody else pays for the power, and you have no
> source of money to buy replacement nodes, you run nodes until they die.
> All the "usual" CBAs assume a constant flow of support moneys for new
> nodes, and that is not always the case.
>> -- greg
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