On Tue, 02 Feb 2010 10:11:03 -0500 Bill Davidsen <davidsen@xxxxxxx> wrote: > 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. > That doesn't make it less reliable. It just makes it more confusing. But for a more complete discussion on raid recovery and when it might be sensible to "vote" among the blocks, see http://neil.brown.name/blog/20100211050355 NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
