Re: /sys/block/md126 still exists even after stopping the array

[NeilBrown <neilb@suse.de>]

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On Tue, 24 Jun 2014 17:38:30 +0200 Francis Moreau <francis.moro@gmail.com>
wrote:

> Hello,
> 
> I'm having the folloing behaviour with kernel 3.14.5 and mdadm v3.3.1.
> 
> After stopping all arrays, I still can see one of them in /sys/block/:
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> md125 : active raid1 sdb3[1] sda3[0]
>       483688448 blocks super 1.2 [2/2] [UU]
>       [======>..............]  resync = 34.9% (169161280/483688448)
> finish=44.0min speed=118852K/sec
>       bitmap: 3/4 pages [12KB], 65536KB chunk
> 
> md126 : active raid1 sdb2[1] sda2[0]
>       4038656 blocks super 1.2 [2/2] [UU]
> 
> md127 : active raid1 sdb1[1] sda1[0]
>       524224 blocks super 1.0 [2/2] [UU]
> 
> unused devices: <none>
> 
> # mdadm --stop /dev/md12[567]
> mdadm: stopped /dev/md125
> mdadm: stopped /dev/md126
> mdadm: stopped /dev/md127
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> unused devices: <none>
> 
> # ls /sys/block/
> md126  sda  sdb  sdc  sr0
> 
> # ls /sys/block/md126/md/
> array_size  array_state  bitmap  chunk_size  component_size  layout
> level  max_read_errors  metadata_version  new_dev  raid_disks
> reshape_direction  reshape_position  resync_start  safe_mode_delay
> 
> # dmesg
> ....
> [ 1573.715476] md125: detected capacity change from 495296970752 to 0
> [ 1573.715626] md: md125 stopped.
> [ 1573.715633] md: unbind<sdb3>
> [ 1573.740681] md: export_rdev(sdb3)
> [ 1573.740694] md: unbind<sda3>
> [ 1573.754008] md: export_rdev(sda3)
> [ 1573.773398] md126: detected capacity change from 4135583744 to 0
> [ 1573.773403] md: md126 stopped.
> [ 1573.773410] md: unbind<sdb2>
> [ 1573.820652] md: export_rdev(sdb2)
> [ 1573.820664] md: unbind<sda2>
> [ 1573.873974] md: export_rdev(sda2)
> [ 1573.889904] md127: detected capacity change from 536805376 to 0
> [ 1573.889910] md: md127 stopped.
> [ 1573.889917] md: unbind<sdb1>
> [ 1573.913978] md: export_rdev(sdb1)
> [ 1573.914033] md: unbind<sda1>
> [ 1573.940627] md: export_rdev(sda1)
> 
> After waiting a couple of min, stopping again md126 worked:
> 
> [ 1835.755661] md: md126 stopped.
> 
> Is this expected ?

No overly surprising.

This is probably caused by udev, or something udev runs, opening /dev/md126
after it has been stopped.  This has the effect of creating an empty inactive
array.
e.g.

 mknod /dev/test b 9 57
 < /dev/test

will make /sys/block/md57 appear.

It is a bit untidy, but shouldn't cause problems.

NeilBrown

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