Perry E. Metzger wrote:
Håkon Bugge <[EMAIL PROTECTED]> writes:
Its even worse. On one mtbd; the BIOS had a menu for enabling ECC; I
did. But reading the register from the chipset revealed nothing was
actually enabled in the hardware. You have to be paranoid in this
business. This was a "bleeding edge" mtbd, with a low revision BIOS of
course. The fu being that a car manufacturer ran a cluster of these
for several months doing crash worthiness simulations ...
So another question is, how can you reliably test any of this stuff?
It isn't like you can reliably induce single bit errors and see if the
hardware catches them. (A special memory module that let you test
.... actually ... you can. Run your code, and have it beat on RAM. We
do this.
Some folks use memtest* and variants, and it catches some base errors.
But it doesn't exercise things the way the application does. So we use
a number of GAMESS runs and other large ram things. Beats the heck out
of the unit. We get a very good indication if it starts tossing MCE
errors that there is a real memory issue.
And, for those doubters, yes, we have caught errors with this that
memtest* did not catch. And yes, we could reliably reproduce them.
All our systems, regardless of their function run with these tests
specifically to try to force MCE errors.
would be a wonderful thing, but I've never even heard of such a thing.)
I'm doing the planning for a new cluster and the whole thing is
remarkably bothersome. You can't easily figure out what motherboards
will even pretend to do ECC that easily, you can't easily check once
you have a sample motherboard in hand. It isn't even easy to get ECC
memory for more modern standards. I'm starting to wonder if doing all
calculations twice, once on each of two machines, isn't easier, but it
seems utterly wrong to do that...
Hmmm.... sounds to me like you probably need to work with groups that
have done this and do this for a living (deliver working systems to
customers, and help them figure out what they need to do). Bug Don
Becker and his team (Penguin), and a bunch of others hanging around here
(and us if you like).
It actually is not hard to build a system with ECC capability. Most
vendors, the vast majority of them, leave the bios default settings and
assume they are "good enough". We don't normally advise that.
Greg L or someone spoke about scrubbing. You can enable that. It is
generally a good idea (we recommend it). Yeah, it does eat memory
bandwidth. And it does slow down access to ram. The is a cost for
every decision.
Perry
--
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: [EMAIL PROTECTED]
web : http://www.scalableinformatics.com
http://jackrabbit.scalableinformatics.com
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