What were you trying to do that didn't work?

While trying to grow md RAID0  with the new device  the md array converted to the RADI4 with clean,degraded state.

Please provide the package NVR for which bug is seen:

[root@localhost ~]# cat /etc/redhat-release 
Red Hat Enterprise Linux release 9.2 (Plow)

[root@localhost ~]# uname -r
5.14.0-427.16.1.el9_4.x86_64

[root@localhost ~]# rpm -qa |grep -i mdadm
mdadm-4.2-8.el9.x86_64

Note: Issue reproducible in RHEL 8.8 as well.

How reproducible:

Steps to reproduce

1.  Created the md RAID0 with the 3 disks.

[root@localhost ~]# lsblk
NAME          MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda             8:0    0 102.4M  0 disk 
sdb             8:16   0 102.4M  0 disk 
sdc             8:32   0 102.4M  0 disk 
sdd             8:48   0 102.4M  0 disk 
sde             8:64   0 102.4M  0 disk 
sr0            11:0    1  1024M  0 rom  
vda           252:0    0    10G  0 disk 
├─vda1        252:1    0     1G  0 part /boot
└─vda2        252:2    0     9G  0 part 
  ├─rhel-root 253:0    0     8G  0 lvm  /
  └─rhel-swap 253:1    0     1G  0 lvm  [SWAP]

[root@localhost ~]# mdadm --create /dev/md101 --level=raid0 --raid-devices=3 /dev/sda /dev/sdb /dev/sdc
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md101 started.

[root@localhost ~]# cat /proc/mdstat 
Personalities : [raid0] 
md101 : active raid0 sdc[2] sdb[1] sda[0]
      307200 blocks super 1.2 512k chunks
      unused devices: <none>

1.  md array created with the above 3 disks with the clean state.

[root@localhost ~]# mdadm -D /dev/md101 
/dev/md101:
           Version : 1.2
     Creation Time : Tue Jun 11 15:11:09 2024
        Raid Level : raid0
        Array Size : 307200 (300.00 MiB 314.57 MB)
      Raid Devices : 3
     Total Devices : 3
       Persistence : Superblock is persistent

       Update Time : Tue Jun 11 15:11:09 2024
             State : clean 
    Active Devices : 3
   Working Devices : 3
    Failed Devices : 0
     Spare Devices : 0

            Layout : unknown
        Chunk Size : 512K

Consistency Policy : none

              Name : localhost.localdomain:101  (local to host localhost.localdomain)
              UUID : 060f4768:8dfac2fc:e13d5108:f9cc2f0d
            Events : 0

    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb
       2       8       32        2      active sync   /dev/sdc

1.  I have added the empty disk /dev/sdd to grow RAID0 by using the below command;

[root@localhost ~]# mdadm --grow /dev/md101 --raid-devices=4 --add /dev/sdd
mdadm: level of /dev/md101 changed to raid4  -----> RAID converted to the RAID4
mdadm: added /dev/sdd
mdadm: Need to backup 6144K of critical section..

[root@localhost ~]# mdadm -D /dev/md101 
/dev/md101:
           Version : 1.2
     Creation Time : Tue Jun 11 15:11:09 2024
        Raid Level : raid4
        Array Size : 409600 (400.00 MiB 419.43 MB)
     Used Dev Size : 102400 (100.00 MiB 104.86 MB)
      Raid Devices : 5
     Total Devices : 4
       Persistence : Superblock is persistent

       Update Time : Tue Jun 11 15:11:51 2024
             State : clean, degraded  ====================> clean,degraded state
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0

        Chunk Size : 512K

Consistency Policy : resync

              Name : localhost.localdomain:101  (local to host localhost.localdomain)
              UUID : 060f4768:8dfac2fc:e13d5108:f9cc2f0d
            Events : 23

    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb
       2       8       32        2      active sync   /dev/sdc
       4       8       48        3      active sync   /dev/sdd
       -       0        0        4      removed  =======> Array showing device in removed state

1. But mdstat showing as a active state.

[root@localhost ~]# cat /proc/mdstat 
Personalities : [raid0] [raid6] [raid5] [raid4] 
md101 : active raid4 sdd[4] sdc[2] sdb[1] sda[0]
      409600 blocks super 1.2 level 4, 512k chunk, algorithm 5 [5/4] [UUUU_]
      
unused devices: <none>

1.  To fix this issue, manually converted above array from RAID4 to RAID0 as below: 

[root@localhost ~]# mdadm --grow --level=0 /dev/md101 --raid-devices=4
mdadm: level of /dev/md101 changed to raid0

[root@localhost ~]# mdadm -D /dev/md101 
/dev/md101:
           Version : 1.2
     Creation Time : Tue Jun 11 15:11:09 2024
        Raid Level : raid0
        Array Size : 409600 (400.00 MiB 419.43 MB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent

       Update Time : Tue Jun 11 15:13:17 2024
             State : clean =========================> clean state
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0

        Chunk Size : 512K

Consistency Policy : none

              Name : localhost.localdomain:101  (local to host localhost.localdomain)
              UUID : 060f4768:8dfac2fc:e13d5108:f9cc2f0d
            Events : 24

    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb
       2       8       32        2      active sync   /dev/sdc
       4       8       48        3      active sync   /dev/sdd
[root@localhost ~]# 

Expected results.

md RAID0 should grow without manual intervation. Why manually need to converted back to RAID 0?

Actual results

md RAID0 array show status as clean,degraded state but $cat /proc/mdstat show active state.