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gpg: Signature made Tue Nov 11 13:11:35 2008 GMT
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Hi,
On Mon, Nov 10, 2008 at 10:32:54PM +0000, Nick Chalk wrote:
> Chris Aitken <cs.aitken@???> wrote:
> >>> RAID-5 is computationally expensive, and as it
> >>> relies on at least three drives as opposed to
> >>> RAID-1's two, it has a shorted MTBF.
> >> Really? Do you have a reference for that?
> > System MTBF = component MTBF/n
> > where n is # of components.
> >
> > So for a component with MTBF of 50k hrs a 2 disk
> > (RAID-1) system has an MTBF of 25k hours, and a
> > 3 disk (RAID-5) system has an MTBF of ~16.7k
> > hrs.
> >
> > During rebuilts the above RAID-1 has an MTBF of
> > 50 k hrs again, and the above RAID-5 has 25k
> > hour MTBF.
>
> I'm replying to Chris' post, as Keith's is saying
> much the same in a different way...
>
> I'm still not following this reasoning. If the
> above is true, RAID is pointless.
The MTBF quoted above is for the failure of any component device,
not of the RAID itself.
It can be an interesting figure since running degraded is often
painful and/or risky.
Cheers,
Andy
