Date: Mon, 27 Oct 1997 07:55:48 -0500 (EST) From: Thomas David Rivers <rivers@dignus.com> To: perlsta@cs.sunyit.edu, tom@sdf.com Cc: hackers@FreeBSD.ORG Subject: Re: Parity Ram Message-ID: <199710271255.HAA02897@lakes.dignus.com>
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> On Sun, 26 Oct 1997, Alfred Perlstein wrote: > > > > > Do you know anything of Richard Hamming's assertion that parity memory > > > > (the old fashioned even/odd type) is-a-bad -thing in large > > > > configurations? > > > > > > I think it bullshit. I've never heard of this before. Nor have you in > > > the two times you've mentioned it, actually stated what is supposed to be > > > so bad about it. > > > > more bits means more chance of error even if they are "error-correcting" > > bits? > > And how is that bad? Even simple parity systems will catch 100% of all > single bit errors, regardless of where the bit appears. > > More bits mean more redundancy. That means it gets safer, not riskier. > > Tom > > In reliability - more doesn't always mean safer. Say, for example, I spread my database across two disks - but both have to be running for the software to gain access. Then, I've just doubled the probability of failure; not halved it. But - if I don't spread things out; but increase redundancy, I may have improved the situation. It depends on the path to the data (recall your database theory - you need one way to access information, redundancy in access paths can cause serious problems as well.) - Dave Rivers -
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