Re: Bugreport: mdmon will not start with latest git version when using ddf container

[NeilBrown <neilb@suse.de>]

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On Wed, 31 Jul 2013 20:14:18 +0200 Albert Pauw <albert.pauw@gmail.com> wrote:

> Seems mdmon will not start when I create a ddf container with raid 
> devices therein:
> 
> I am using this version from git:
> 
> mdadm - v3.3-rc2-20-gd81cc6a - 31st July 2013
> 
> on Centos 6.4, 2.6.32-358.14.1.el6.x86_64
> 
> I am using 5 loop devices of 512 MB each for disks.
> I created a container with 5 disks:
> 
> mdadm -CR /dev/md127 -e ddf -l container -n 5 /dev/loop[1-5]
> 
> [root@moonlight ~]# cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid1]
> md127 : inactive loop5[4](S) loop4[3](S) loop3[2](S) loop2[1](S) loop1[0](S)
>        163840 blocks super external:ddf
> 
> unused devices: <none>
> 
> And created two raid sets in it, one with three disks in raid 5, the 
> other a raid 1
> 
> [root@moonlight ~]# mdadm -CR /dev/md1 -l raid5 -n 3 /dev/md127
> mdadm: array /dev/md1 started.
> mdadm: failed to launch mdmon. Array remains readonly
> [root@moonlight ~]# cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid1]
> md1 : active (read-only) raid5 loop1[2] loop2[1] loop3[0]
>        958464 blocks super external:/md127/1 level 5, 512k chunk, 
> algorithm 2 [3/3] [UUU]
>            resync=PENDING
> 
> md0 : active (read-only) raid1 loop4[1] loop5[0]
>        479232 blocks super external:/md127/0 [2/2] [UU]
>            resync=PENDING
> 
> md127 : inactive loop5[4](S) loop4[3](S) loop3[2](S) loop2[1](S) loop1[0](S)
>        163840 blocks super external:ddf
> 
> unused devices: <none>
> 
> And adding another one, raid5 in my case, gives the same result for the 
> next /dev/md device.
> 
> Unfortunately, they stay readonly, as mdmon won't start, so mdadm 
> --readwrite /dev/md0, etc, won't work.
> 
> However, when I create these raid devices directly on top of the 
> /dev/loop[1-5] devices, without using a ddf container, it works as 
> advertised and the devices get (re)build/resynced.
> 

Thanks for the report.
This works when I try it so we must be doing something slightly differently.

When mdadm tries to run mdmon it looks in:
  - the same directory that 'mdadm' was found in
  - /sbin
  - the current directory.

Where are mdadm and mdmon installed?  What directory are you running from.
If we can't discover the problem from that information, please run
   strace -f -o /tmp/md-trace mdadm -CR /dev/md1 -l raid5 -n 3 /dev/md127

and post the resulting /tmp/md-trace file.

Thanks,
NeilBrown

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