[Beowulf] Re: Cooling vs HW replacement

Greg Lindahl lindahl at pathscale.com
Mon Jan 24 02:14:14 EST 2005


On Mon, Jan 24, 2005 at 01:57:16AM -0500, Robert G. Brown wrote:

> Otherwise, what I was basically doing is describing the bathtub

Didn't look like that to me, but I just read your rants, I wasn't the
guy who wrote them.

> As was pointed out by Karen (and I agree) the mfr warranty period is
> perhaps a better number for most people to pay attention to than MTBF

I disagree. The warranty period tells you about disk lifetime. The
MTBF tells you about the failure rate in the bottom of the
bathtub. These are nearly independent quantities; I already pointed
out that the fraction of disks which fail in the bottom of the bathtub
is small, even if you multiply it by 2X or 3X. So the major factor in
the price and length of that warranty is the lifetime.

Lifetime and MTBF are simply different measures. Depending on what you
are thinking about, you pay attention to one or the other or neither.

> His point (I think) was that statistics are lovely
> but use your gut and your head as well -- reality check time.

Yes. And I have yet to see anything in your complaint that is anything
but misinterpretation on your part. Reality check time, indeed. You
can't use MTBF by itself as a measure of quality, period, so complaining
that it isn't a good single item to measure disk quality is, well,
operator error.

-- greg

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