On 12/08/16 02:32, NeilBrown wrote: > On Sun, Aug 07 2016, Wols Lists wrote: > >> On 07/08/16 01:32, Glenn Enright wrote: >>> On 7/08/2016 12:01 pm, "Wols Lists" <antlists@xxxxxxxxxxxxxxx >>> <mailto:antlists@xxxxxxxxxxxxxxx>> wrote: >>>> >>>> On 05/08/16 21:16, Wols Lists wrote: >>>>> In my testing of xosview, I've been mucking about with a vm and raid. >>>>> xosview is looking quite promising (I've got a few comments about it, >>>>> but never mind). >>>>> >>>>> BUT. In mucking about with raid 1, I increased my raid devices to three. >>>>> I now just can NOT convert the array to raid 5! I've been mucking around >>>>> with all sorts of things trying to get it to work, but finally two error >>>>> messages make things clear. >>>>> >>>> Following up to myself - suddenly thought "I know what's wrong". So I >>>> stopped the array, and of course couldn't access it, it was no longer >>>> there. So I assembled but didn't run it, and it worked fine. >>>> >>>> Simples, once you realise what's wrong - you can ADD devices to a >>>> running array, but you can't REMOVE them. >>>> >>>> Cheers, >>>> Wol >>>> >> >>> >>> You can remove em if you mark em as failed first. Eg >>> >>> Mdadm /dev/mdx --fail /dev/sdc1 --remove /dev/sdc1 >>> >>> Best, Glenn >>> >> Except - if you read my original post - I was trying to TOTALLY remove >> the device! >> >> mdadm --grow -raid-devices=2 >> >> THAT was the problem - I had a 3-device mirror, and you can't convert >> that to raid5! Even if you've --fail --remove'd the third device! >> >> In other words, "--grow --raid-devices=more" will work on a running >> device, "--grow --raid-devices=less" will only work on an array that is >> built but not running. > > I don't believe this is correct, and I could reproduce your results in > quick tests. > > If the array is not running, then you cannot reshape it at all. > > You can reduce the number of devices in a RAID1 at any time as long as > the number of active devices is not greater than the number of devices > requested. > > /dev/md0 has 3 working devices: > > # mdadm -G /dev/md0 -n2 > mdadm: failed to set raid disks > # mdadm /dev/md0 -f /dev/loop0 > mdadm: set /dev/loop0 faulty in /dev/md0 > # mdadm -G /dev/md0 -n2 > raid_disks for /dev/md0 set to 2 > That's my error - you've done pretty much exactly the same as me, except my second try also failed, whereas yours has succeeded. Why? (although I did --fail, --remove). > >> >> I now have the problem that my "--grow --level=5" has fallen foul of the >> "reshape stuck at zero" problem, and I can now neither run the array, >> nor get the reshape working ... :-( > > We really need to fix this ... if only I knew how to reproduce it. Mikael gave me the force-revert-reshape syntax, which worked a treat when I did it his way (I'd tried to do it already, but obviously didn't get the magic incantation right :-) > As you'll see from my other thread, this is a test array (I was trying to test the new raid features of xosview :-), so there's no urgency from my point of view, but yes, I want to know what's going wrong, too. I want to write all this up as documentation :-) My problem is I've only got one computer with decent-enough grunt to run the VM, and getting uninterrupted access to it (wife, two grand-kids) isn't always easy. I'll get back to it asap - Mikael is on the case, but I need to reset it back the way it was and try the reshape again. I hope it's not the SuSE kernel - I'm running the latest mdadm from your git repository. > NeilBrown > 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
