Date: Wed, 24 Nov 2004 18:11:15 +0100 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Eirik ?verby <ltning@anduin.net> Cc: stable@freebsd.org Subject: Re: graid3 - requirements or manpage wrong? Message-ID: <20041124171115.GP7232@darkness.comp.waw.pl> In-Reply-To: <41A45A3F.5010008@anduin.net>
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[-- Attachment #1 --] On Wed, Nov 24, 2004 at 10:54:07AM +0100, Eirik ?verby wrote: +> to the best of my ability I have been investigating the 'real' +> requirements of a raid-3 array, and cannot see that the following text +> from graid3(8) cannot possibly be correct - and if it is, then the +> implementation must be wrong or incomplete (emphasis added): +> +> label Create a RAID3 device. The last given component will contain +> parity data, all the rest - regular data. ***Number of +> compo- +> nents has to be equal to 3, 5, 9, 17, etc. (2^n + 1).*** +> +> I might be wrong, but I cannot see how a raid-3 array should require +> (2^n + 1) drives - I am fairly certain I have seen raid-3 arrays +> consisting of four drives, for example. This is also what I had hoped to +> accomplish. This requirement is because we want sectorsize to be power of 2 (UFS needs it). In RAID3 we want to send every I/O request to all components at once, that's why we need sector size to be N*512, where N is a power of 2 value AND because graid3 uses one parity component we need N+1 providers. -- Pawel Jakub Dawidek http://www.FreeBSD.org pjd@FreeBSD.org http://garage.freebsd.pl FreeBSD committer Am I Evil? Yes, I Am! [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFBpMCzForvXbEpPzQRAqthAJ9xhpChtjETn6GxPEMYyM3hut8qfQCdFbET WI48BnLk1RSaNukg/38V5qg= =AKqe -----END PGP SIGNATURE-----home | help
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