Cheap PCs from Wal-Mart

Mark Hahn hahn at
Sun Jun 1 16:56:02 EDT 2003

> I had not read of the Via chips and had been planning to use the AMD Athlon
> chips. Are the via chips ok? Will they run linux/mosix ok? Any specific
> thoughts about them?

they're fairly slow, from what I've read, and still use the P5 pinout
(which means you'll peak at around 500 MB/s).  the chip is optimized 
for area/power/price first, not performance - VIA's been pushing it for
use in embedded/appliance kinds of uses.

there's nothing inherently wrong with using lots of low-power (both ways)
chips.  if you carefully evaluate your code, and find that higher-powered
chips don't help much (for instance, you aren't actually bottlenecked on 
FP or memory bandwidth, or are drastically parallel.)  as I see it, even if
Amdahl's saw lets you take this path, you wind up spending more and more
on non-computational hardware.

for instance, compare:
	"light": 1U via/PIII-class server, $170 1U chassis
	- probably cheaper per unit.
	- probably cooler per unit.

	"heavy": 1U dual Xeon/Opteron server, $350 1U chassis
	- definitely faster (CPU, cache, dram, network).
	- definitely more reliable.
	- probably denser.
	- definitely hotter per unit.
	- definitely more expensive per unit.

I consider heat the only serious issue with the 'heavy' approach, and there's 
just not much we can do about that except hold our breath for .09 ;)
like heat, reliability is a huge concern mainly for large clusters - you 
definitely don't want 512 noname powersupplies, or the kind of chassis 
where the vendor doesn't realize that extra fans are a liability.

it's easy to imagine situations where the light approach would win:
a small, non-critical learning cluster, for instance, with not much space
available, or cooling capacity.  or even a google-ish DB-ish thing where 
you're really trying to make smart disk drives.  some place with plentiful
cheap labor.

an interesting recent development is non-wimpy blade systems.  the original
blades had all the disadvantages of 'light' above, but also were extremely
expensive and utterly proprietary.

'heavy blades' seem to be based on commodity motherboards (good), but 
apparently with a separate powersupply for each board (bad).  I'd like 
to see someone market a redundant PS which could power several motherboards
(not unlike the way minis and mainframes often use DC distribution).
the motherboards would still be standard/commodity/non-proprietary,
and could even have passive CPU heatsinks, and just a minimal tray to 
screw each MB onto.

using wallmart PCs for "light" cluster nodes seems sensible to me, assuming
they do actually have reasonable reliability.  again, assuming density isn't 
an issue for you, and your code is happy with slow CPUs...

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