[Beowulf] RE: Capitalization Rates - How often should you replace a cluster? (resent - 1st sending wasn't posted ).

Greg Lindahl lindahl at pbm.com
Tue Jan 20 02:35:36 EST 2009

On Tue, Jan 20, 2009 at 08:14:35AM +0100, Jon Aquilina wrote:

> in all honesty is there a need really to replace the cluster. why not just
> add onto it?

Think about it: if you pay 1/3 the cost of a new node per year in rent
and utilities, and nodes get twice as fast for the same cost every 18
months. Let's say that means each year performance increases by 60%
(close enough for our purposes.)

Year 1: I pay 1.33$ for 1 unit of performance
Year 2: I pay 0.33$ for 1 unit of performance -- or 1.33$ for 1.6 units of performance
Year 3: I pay 0.33$ for 1 unit of performance -- or 1.33$ for 2.56 units of performance
Year 4: I pay 0.33$ for 1 unit of performance -- or 1.33$ for 4.1 units of performance

Hey! In year 4 it's about the same to keep the old cluster, or throw
it out and buy a new one. (If I want to spend the same $$, I can buy a
cluster 1/4 the size, but same performance, as the original one.)

And in year 5, it's a big win to buy the new stuff.

If you don't pay rent and utilities, then sure, you'll probably keep
as much junk as will fit in whatever space you have. Maybe the cluster
I put together in 1998 at UVa is still running...

-- greg

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