On Mon 10 Aug 2015 07:10:55 PM Wols Lists wrote: > On 10/08/15 18:44, Thomas Fjellstrom wrote: > > On Mon 10 Aug 2015 11:35:13 AM Mikael Abrahamsson wrote: > >> On Sat, 8 Aug 2015, Thomas Fjellstrom wrote: > >>> I did try that :( It fails to assemble because it only sees sdc as a > >>> spare. > >>> Maybe because I did things with the old mdadm first, and did a --remove? > >>> That seems to have wiped out the "slot" information (it's -1) so the > >>> assemble force magic can't figure things out? Just a guess on my part. > >> > >> Unless someone else has a better idea, I'd say you're right. If you would > >> have unplugged the failed drive (so it disappeared completely), it could > >> probably have been re-added. So unless you have a copy of the old > >> superblock, your only way to proceed now is to use --create > >> --assume-clean > >> and get all the parameters right (order, offsets etc). There are lots of > >> examples in the mailing list archives of people trying this and some > >> actually suceeding. > > > > I think the only thing that would stop that from working is that there is > > data in the bitmap. So if a assume clean is done, it might ignore that > > and cause some extra corruption? > > Which is why you use loopback devices. You'll need to look back at > previous posts to see how to do it, but you put a pseudo-layer over the > real disks (which never actually get written to), and you can then fsck > your array. If that comes up clean, you know you got the assemble > parameters right, and you can shut down the pseudo-array and assemble > the real array. > > > It'd be interesting to figure out if i can set that slot number manually > > or > > with a tool. That might be a smarter/safer way of doing it. > > Better the pseudo way (which will definitely allow you to recover IF the > disk isn't corrupted) than trying your own stuff which might write to > the disk and make life harder/impossible to recover. Yeah, I did that once previously for a recovery. It was quite handy. I backed everything up to a different machine. And re-created the array. I may do that again. But then I actually have a mostly full backup, about the only things i care about is some pictures I added to the array before it went down, that I still have a copy of, but would have to copy them all back off of various devices. > Cheers, > Wol -- Thomas Fjellstrom thomas@xxxxxxxxxxxxx -- 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
