On Thu, Dec 11, 2014 at 10:01:06PM -0800, Robert White wrote: > So RAID5 with three media M is > > M MM MMM > D1 D2 P(a) > D3 P(b) D4 > P(c) D5 D6 RAID5 with two media is well defined, and looks like this: M MM D1 P(a) P(b) D2 D3 P(c) With even parity and N disks P(a) ^ D1 [^ D2 ^ ... ^ DN] = 0 Simplifying for one data disk and one parity stripe: P(a) ^ D1 = 0 therefore P(a) = D1 which is effectively (and, in practice, literally) mirroring.
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