Re: [PATCH] mdadm: fix reshape from RAID5 to RAID6 with backup file

["Tkaczyk, Mariusz" <mariusz.tkaczyk@xxxxxxxxxxxxxxx>]

On 16.03.2021 16:59, Nigel Croxon wrote:
> ----- Original Message -----
> From: "Mariusz Tkaczyk" <mariusz.tkaczyk@xxxxxxxxxxxxxxx>
> To: "Jes Sorensen" <jes@xxxxxxxxxxxxxxxxxx>, "Nigel Croxon" <ncroxon@xxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xni@xxxxxxxxxx
> Sent: Tuesday, March 16, 2021 10:54:22 AM
> Subject: Re: [PATCH] mdadm: fix reshape from RAID5 to RAID6 with backup file
>
> Hello Nigel,
>
> Blame told us, that yours patch introduce regression in following
> scenario:
>
> #mdadm -CR imsm0 -e imsm -n4 /dev/nvme[0125]n1
> #mdadm -CR volume -l0 --chunk 64 --raid-devices=1 /dev/nvme0n1 --force
> #mdadm -G /dev/md/imsm0 -n2
>
> At the end of reshape, level doesn't back to RAID0.
> Could you look into it?
> Let me know, if you need support.
>
> Thanks,
> Mariusz
>
> I’m trying your situation without my patch (its reverted) and I’m not seeing success.
> See the dmesg log.
>
>
> [root@fedora33 mdadmupstream]# mdadm -CR volume -l0 --chunk 64 --raid-devices=1 /dev/nvme0n1 --force
> mdadm: /dev/nvme0n1 appears to be part of a raid array:
>        level=container devices=0 ctime=Wed Dec 31 19:00:00 1969
> mdadm: Creating array inside imsm container md127
> mdadm: array /dev/md/volume started.
>
> [root@fedora33 mdadmupstream]# cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid0]
> md126 : active raid0 nvme0n1[0]
>       500102144 blocks super external:/md127/0 64k chunks
>
> md127 : inactive nvme3n1[3](S) nvme2n1[2](S) nvme1n1[1](S) nvme0n1[0](S)
>       4420 blocks super external:imsm
>
> unused devices: <none>
> [root@fedora33 mdadmupstream]# mdadm -G /dev/md/imsm0 -n2
> [root@fedora33 mdadmupstream]# cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid0]
> md126 : active raid4 nvme3n1[2] nvme0n1[0]
>       500102144 blocks super external:-md127/0 level 4, 64k chunk, algorithm 5 [2/1] [U_]
>
> md127 : inactive nvme3n1[3](S) nvme2n1[2](S) nvme1n1[1](S) nvme0n1[0](S)
>       4420 blocks super external:imsm
>
> unused devices: <none>
>
>
> dmesg says:
> [Mar16 11:46] md/raid:md126: device nvme0n1 operational as raid disk 0
> [  +0.011147] md/raid:md126: raid level 4 active with 1 out of 2 devices, algorithm 5
> [  +0.044605] md/raid0:md126: raid5 must have missing parity disk!
> [  +0.000002] md: md126: raid0 would not accept array
>
> -Nigel
Hello Nigel,
It looks strange. Could you try to reproduce it with --size, less than
smaller drive in array (e.g. 10G)?

If it doesn't help please provide me your kernel version. I will try to
reproduce it myself.

Thanks,
Mariusz