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 [EMAIL PROTECTED] http://garage.freebsd.pl FreeBSD committer Am I Evil? Yes, I Am!
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