From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: mismatch_cnt questions Date: Fri, 09 Mar 2007 00:20:11 -0500 Message-ID: <45F0EE8B.2020004@tmr.com> References: <17898.45673.573800.56474@notabene.brown> <45EB3867.8050907@eyal.emu.id.au> <17899.18568.523543.478792@notabene.brown> <45EBCA83.40106@eyal.emu.id.au> <17900.43653.510415.553440@notabene.brown> <45EFAFB8.3070703@zytor.com> <45F0BFBA.5010201@tmr.com> <45F0E094.4060809@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <45F0E094.4060809@zytor.com> Sender: linux-raid-owner@vger.kernel.org To: "H. Peter Anvin" Cc: "Martin K. Petersen" , Neil Brown , Eyal Lebedinsky , Christian Pernegger , linux-raid@vger.kernel.org List-Id: linux-raid.ids H. Peter Anvin wrote: > Bill Davidsen wrote: >> >> When last I looked at Hamming code, and that would be 1989 or 1990, I >> believe that I learned that the number of Hamming bits needed to >> cover N data bits was 1+log2(N), which for 512 bytes would be 1+12, >> and fit into a 16 bit field nicely. I don't know that I would go that >> way, fix any one bit error, detect any two bit error, rather than a >> CRC which gives me only one chance in 64k of an undetected data >> error, but I find it interesting. >> > > A Hamming code across the bytes of a sector is pretty darn pointless, > since that's not a typical failure pattern. I just thought it was perhaps one of those little known facts that meaningful ECC could fit in 16 bits. I mentioned that I wouldn't go that way, mainly because it would be less effective catching multibit errors. This was a "fun fact" for all those folks who missed Hamming codes in their education, because they are old tech. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979