On Tue, 3 Jun 2025 17:46:01 +0100 Wol <antlists@xxxxxxxxxxxxxxx> wrote: > On 03/06/2025 02:05, David Niklas wrote: > > So I setup the array into read-only mode and started the array with > > only two of the drives. Drives 0 and 1. Then I proceeded to try and > > start a second pair, drives 2 and 3, so that I could scan them > > simultaneously. With the intent of then switching it over to 0 and 2 > > and 1 and 3, then 0 and 3 and 1 and 2. > > BACKUP! BACKUP!! BACKUP!!! It's when I was trying to make my yearly backup that I found out it was corrupting. I have HDDs I backup to. When I backup, I erase the previous year (as I don't have enough room otherwise), then backup the new year. As a system, it worked up until now. > Is your array that messed up that it won't assemble? If you can just > get it to assemble normally that's your best bet by far. Trying to > assemble it as two pairs is throwing away the whole point of a raid 6! It assembles fine with all the disks, the problem is the data corruption that has occurred across the members. > And make sure you know the order of the drives in the array! I hope you > haven't lost that infof. Everything is written down on paper. > If your event counts are all similar, then you'll hopefully recover > most of your data. Your biggest worry will be the mobo and ram having > trashing an in-flight write that corrupts the disk. Yes, that's my problem. I wanted to try and isolate the disk pairs so that I could try and figure out if there is any pattern or differing copies that would allow me to restore the corrupted data. > Then once you've got the array assembled, I can't remember the command, > but there is a command that will read the entire stripe, check the > paritIES - both of them, and recreate the data. If that fails, your > data is probably toast, and nothing you can do will be able to retrieve > much :-( > > Cheers, > Wol > Searching online turned up raid6check. https://unix.stackexchange.com/questions/137384/raid6-scrubbing-mismatch-repair But the people there also pointed out that Linux's raid repair operation only recalculates the parity. I would have thought that it did a best of 3 option. I mean, that's a big part of why we have RAID6 instead of RAID5, right? I think you misunderstood my original question, how do I assemble the RAID6 pairs (RO mode) into two different arrays such that I can read from them simultaneously? If I have to do some coding with respect to the mdadm utility, I'm willing. But for all I know, the Linux Kernel might destroy all of my data if I try something like that. Thanks, David
