Jeff Bonwick wrote:
For 6 disks, 3x2-way RAID-1+0 offers better resiliency than RAID-Z
or RAID-Z2.
Maybe I'm missing something, but it ought to be the other way around.
With 6 disks, RAID-Z2 can tolerate any two disk failures, whereas
for 3x2-way mirroring, of the (6 choose 2) = 6*5/2 = 15 possible
two-disk failure scenarios, three of them are fatal.
For the 6-disk case, with RAID-1+0 you get 27/64 surviving states
versus 22/64 for RAID-Z2. This accounts for the cases where you could
lose 3 disks and survive with RAID-1+0.
-- richard
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