On 09/09/17 18:42, Marc MERLIN wrote:
Do we also agree that "mistmatch sector" means that the parity does not add up, and that in a raid5 scenario, the md layer has no idea which of the drives has bad data, just that things don't add up?
Yes. Raid 5 only protects you from a disk failure. With one parity block, you can only solve the equation for one unknown, ie for a missing block (drive). If a block is corrupt, that gives you two unknowns - which block is corrupt and what the correct value should be. With raid-6 you have two parity blocks so can solve for two unknowns ie one random corrupt block OR two drive failures.
But with raid 5 you can only solve for a missing/corrupt block IF you can tell the system which one is messed up. Btrfs is telling you that the data is fine, so you know it's the parity, and raid 5 can fix that for you.
Cheers, Wol -- 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
