I’m trying your situation without my patch (its reverted) and I’m not seeing success.
[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
> On Mar 16, 2021, at 10:54 AM, Tkaczyk, Mariusz <mariusz.tkaczyk@xxxxxxxxxxxxxxx> wrote:
>
> 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
>
