----- Original Message -----

From: "Xiao Ni" <redacted>
To: "NeilBrown" <redacted>
Cc: linux-raid@vger.kernel.org
Sent: Thursday, May 21, 2015 11:37:57 AM
Subject: Re: raid5 reshape is stuck



----- Original Message -----

quoted

From: "NeilBrown" <redacted>
To: "Xiao Ni" <redacted>
Cc: linux-raid@vger.kernel.org
Sent: Thursday, May 21, 2015 7:48:37 AM
Subject: Re: raid5 reshape is stuck

On Fri, 15 May 2015 03:00:24 -0400 (EDT) Xiao Ni [off-list ref] wrote:

quoted

Hi Neil

   I encounter the problem when I reshape a 4-disks raid5 to raid5. It
   just
   can
appear with loop devices.

   The steps are:

[root@dhcp-12-158 mdadm-3.3.2]# mdadm -CR /dev/md0 -l5 -n5 /dev/loop[0-4]
--assume-clean
mdadm: /dev/loop0 appears to be part of a raid array:
       level=raid5 devices=6 ctime=Fri May 15 13:47:17 2015
mdadm: /dev/loop1 appears to be part of a raid array:
       level=raid5 devices=6 ctime=Fri May 15 13:47:17 2015
mdadm: /dev/loop2 appears to be part of a raid array:
       level=raid5 devices=6 ctime=Fri May 15 13:47:17 2015
mdadm: /dev/loop3 appears to be part of a raid array:
       level=raid5 devices=6 ctime=Fri May 15 13:47:17 2015
mdadm: /dev/loop4 appears to be part of a raid array:
       level=raid5 devices=6 ctime=Fri May 15 13:47:17 2015
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@dhcp-12-158 mdadm-3.3.2]# mdadm /dev/md0 -a /dev/loop5
mdadm: added /dev/loop5
[root@dhcp-12-158 mdadm-3.3.2]# mdadm --grow /dev/md0 --raid-devices 6
mdadm: Need to backup 10240K of critical section..
[root@dhcp-12-158 mdadm-3.3.2]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 loop5[5] loop4[4] loop3[3] loop2[2] loop1[1] loop0[0]
      8187904 blocks super 1.2 level 5, 512k chunk, algorithm 2 [6/6]
      [UUUUUU]
      [>....................]  reshape =  0.0% (0/2046976)
      finish=6396.8min
      speed=0K/sec
      
unused devices: <none>

   It because the sync_max is set to 0 when run the command --grow

[root@dhcp-12-158 mdadm-3.3.2]# cd /sys/block/md0/md/
[root@dhcp-12-158 md]# cat sync_max
0

   I tried reproduce with normal sata devices. The progress of reshape is
   no problem. Then
I checked the Grow.c. If I use sata devices, in function reshape_array,
the
return value
of set_new_data_offset is 0. But if I used loop devices, it return 1.
Then
it call the function
start_reshape.

set_new_data_offset returns '0' if there is room on the devices to reduce
the
data offset so that the reshape starts writing to unused space on the
array.
This removes the need for a backup file, or the use of a spare device to
store a temporary backup.
It returns '1' if there was no room for relocating the data_offset.

So on your sata devices (which are presumably larger than your loop
devices)
there was room.  On your loop devices there was not.

quoted

   In the function start_reshape it set the sync_max to reshape_progress.
   But in sysfs_read it
doesn't read reshape_progress. So it's 0 and the sync_max is set to 0.
Why
it need to set the
sync_max at this? I'm not sure about this.

sync_max is set to 0 so that the reshape does not start until the backup
has
been taken.
Once the backup is taken, child_monitor() should set sync_max to "max".

Can you  check if that is happening?

Thanks,
NeilBrown

  Thanks very much for the explaining. The problem maybe is fixed. I tried
  reproduce this with newest
kernel and newest mdadm. Now the problem don't exist. I'll do more tests and
give the answer above later.

Hi Neil

   As you said, it doesn't enter child monitor. The problem still exist.

The kernel version :
[root@intel-canoepass-02 tmp]# uname -r
4.0.4

mdadm I used is the newest git code from git://git.neil.brown.name/mdadm.git

   
   In the function continue_via_systemd the parent find pid is bigger than 0 and
status is 0. So it return 1. So it have no opportunity to call child_monitor.


   And if it want to set sync_max to 0 until the backup has been taken. Why does not 
set sync_max to 0 directly, but use the value reshape_progress? There is a little confused.

Best Regards
Xiao