[geeks] Fwd: [IP] Interesting speculation on the tech behind gmail

[Lionel Peterson]

> From: adh at an.bradford.ma.us (Sandwich Maker)
> Date: 2004/04/07 Wed PM 08:54:03 GMT
> To: geeks at sunhelp.org
> Subject: Re: [geeks] Fwd: [IP] Interesting speculation on the tech behind
gmail
>
> aren't disk mtbf into the 100000h range now? and - assuming
> 73G drives - a 1 petabyte fs would require only ~14000 drives.
> that works out to one disk failure every ~7h. with raid5 and
> hot spares, hardly a crisis.

I don't follow your math... NOT saying you are wrong, but further insight
appreciated.

If a drive has a MTBF of 100K hours, that comes out to what, about 400 24 hour
days, right? Now, some drives may fail immediately (DOA+1 hour), other drives
may last for 200K hours (giving a 100K hour mean), correct?

Rather than a perfect linear failure rate (3 per day, for 400 days), the
presumption is that the failures would tend to cluster around the 400 day
mark, with very few failing in either the first 200 days or the last 200
days... Right?

> mtbf of 100k boards would have to be in the 700000h [the
> better part of a century] to be equal. are they really that
> good?

I would suspect that if the MB relies on a moving part (fan) it is likely to
fail when the fan fails. If it does not rely on moving parts, it *could* run
forever (seemingly)...

Now, the presumption is that Google will actually have light use of each HD,
as they will only be active when one of the (aprox.) 73 people with their 1
gig of emals space on that drive access their account (or when email
arrives)...

Is my logic completely wrong, or nearly right? ;^)

Thanks,


Lionel
lionel 4287 at verizon net