Neil Brown wrote:
On Mon, 01 Feb 2010 16:18:23 -0500
Bill Davidsen <davidsen@xxxxxxx> wrote:
Comment: when there is a three way RAID-1, why doesn't repair *vote* on
the correct value instead of just making a guess?
Because truth is not democratic.
(and I defy you to define "correct" in any general way in this context).
If you are willing to accept that the reconstructed data from RAID-[56]
is "correct" then the data from RAID-1 majority opinion is "correct." If
you say that such recovered data is the "most likely to match what was
written," then data consistent on (N+1)/2 drives of a RAID-1 should be
viewed in the same light. Call it "most likely to be correct" if you
prefer, but picking a value from a drive at random is less likely.
This whole discussion simply shows that for RAID-1 software RAID is less
reliable than hardware RAID (no, I don't mean fake-RAID), because it
doesn't pin the data buffer until all copies are written.
--
Bill Davidsen <davidsen@xxxxxxx>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein
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