Re: Oracle and Raid setup

Frank van Bortel <frank.van.bortel_at_gmail.com> wrote:
> Noons wrote:
> > Cris Carampa apparently said,on my timestamp of 9/06/2005 4:41 PM:
> >
> >>
> >> But Raid 1 gives you only fault tolerance, no performance gains
> >> because there is no striping. Or am I wrong?
> >
> >
> > Absolutely right. In fact, it is slower for writes...
> >
>
> Why would a mirrored write be slower for writes? OK, as slow
> as the slowest disk, but those differences can (should!) only
> be marginal.

If each write takes a random amount of time uniformly distributed between 0 and 1 (in whatever units of time would make sense), then the average wait for one write is 0.5, while the average wait for slower of two writes is 0.6667. That is a 33% penalty. I don't know if that qualifies as marginal or not. I don't know what a realistic actual distribution of write delays is, but I think uniform from 0 to 1 is not too outrageous of an assumption.

Xho

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