Re: [PATCH 3/3] raid5: introduce MD_BROKEN

On Fri, 25 Feb 2022 15:22:00 +0800
Guoqing Jiang [off-list ref] wrote:

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If one member disk was set Faulty which caused BROKEN was set, is
it possible to re-add the same member disk again?
 

Is possible to re-add drive to failed raid5 array now? From my
understanding of raid5_add_disk it is not possible.  

I mean the below steps, it works as you can see.

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[root@vm ~]# echo faulty > /sys/block/md0/md/dev-loop1/state
[root@vm ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 loop2[2] loop1[0](F)
        1046528 blocks super 1.2 level 5, 512k chunk, algorithm 2
[2/1] [_U] bitmap: 0/1 pages [0KB], 65536KB chunk

unused devices: <none>
[root@vm ~]# echo re-add > /sys/block/md0/md/dev-loop1/state
[root@vm ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 loop2[2] loop1[0]
        1046528 blocks super 1.2 level 5, 512k chunk, algorithm 2
[2/2] [UU] bitmap: 0/1 pages [0KB], 65536KB chunk

unused devices: <none>

In this case array is not failed (it is degraded). For that reason I
think that my changes are not related.

# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid1] [raid10]
md127 : active raid5 nvme5n1[1] nvme4n1[0](F)
      5242880 blocks super 1.2 level 5, 512k chunk, algorithm 2 [2/1]
[_U]

unused devices: <none>
# cat /sys/block/md127/md/array_state clean

# mdadm -D /dev/md127
/dev/md127:
           Version : 1.2
     Creation Time : Thu Mar  3 18:49:53 2022
        Raid Level : raid5
        Array Size : 5242880 (5.00 GiB 5.37 GB)
     Used Dev Size : 5242880 (5.00 GiB 5.37 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

       Update Time : Thu Mar  3 18:52:46 2022
             State : clean, degraded
    Active Devices : 1
   Working Devices : 1
    Failed Devices : 1
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : resync

              Name : gklab-localhost:vol  (local to host
              gklab-localhost)
              UUID : 711594e8:73ef988c:87a85085:b30c838d
            Events : 8

    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       1     259        9        1      active sync   /dev/nvme5n1

       0     259        5        -      faulty   /dev/nvme4n1


Do I miss something?

Thanks,
Mariusz