mdadm: can't removed failed/detached drives when using metadata 1.x

Hi Neil,

I recently came across what I believe is a regression in mdadm, which
has been introduced in version 3.1.3.

It seems that, when using metadata 1.x, the handling of failed/detached
drives isn't effective anymore.

Here's a quick example:

[root@GrosCinq ~]# mdadm -C /dev/md4 -l1 -n2 --metadata=1.0 /dev/sdc1 /dev/sdd1
mdadm: array /dev/md4 started.
[root@GrosCinq ~]#
[root@GrosCinq ~]# mdadm --wait /dev/md4
[root@GrosCinq ~]#
[root@GrosCinq ~]# mdadm -D /dev/md4
/dev/md4:
        Version : 1.0
  Creation Time : Thu Feb 10 13:56:31 2011
     Raid Level : raid1
     Array Size : 1953096 (1907.64 MiB 1999.97 MB)
  Used Dev Size : 1953096 (1907.64 MiB 1999.97 MB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Thu Feb 10 13:56:46 2011
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : GrosCinq:4  (local to host GrosCinq)
           UUID : bbfef508:252e7ce1:c95d4a03:8beb3cbd
         Events : 17

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sdc1
       1       8       49        1      active sync   /dev/sdd1

[root@GrosCinq ~]# mdadm --fail /dev/md4 /dev/sdc1
mdadm: set /dev/sdc1 faulty in /dev/md4
[root@GrosCinq ~]#
[root@GrosCinq ~]# mdadm -D /dev/md4 | tail -n 6

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       49        1      active sync   /dev/sdd1

       0       8        1        -      faulty spare   /dev/sdc1
[root@GrosCinq ~]#
[root@GrosCinq ~]# mdadm --remove /dev/md4 failed
[root@GrosCinq ~]#
[root@GrosCinq ~]# mdadm -D /dev/md4 | tail -n 6

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       49        1      active sync   /dev/sdd1

       0       8        1        -      faulty spare   /dev/sdc1
[root@GrosCinq ~]#

This is with mdadm 3.1.4, 3.1.3 or even 3.2, but not 3.1.2. I did a git bisect to try and isolate the regression and it appears the guilty commit is :

b3b4e8a : "Avoid skipping devices where removing all faulty/detached
           devices."

As stated in the commit, this is only true with metadata 1.x. With 0.9, there is no problem. I also tested with detached drives as well as raid5/6 and encountered the same issue. Actually, with detached drives, it's even more annoying, since using --remove detached is the only way to remove the device without restarting the array. For a failed drive, there is still the possibility to use the device name.

Do you have any idea of the reason behind that regression ? Shall this patch only apply in the case of 0.9 metadata ?

Regards,

-- 
Rémi
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