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I have /dev/md127 RAID5 array that consisted of four drives. I managed to hot remove them from the array and currently /dev/md127 does not have any drives:

cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sdd1[0] sda1[1]
      304052032 blocks super 1.2 [2/2] [UU]

md1 : active raid0 sda5[1] sdd5[0]
      16770048 blocks super 1.2 512k chunks

md127 : active raid5 super 1.2 level 5, 512k chunk, algorithm 2 [4/0] [____]

unused devices: <none>


mdadm --detail /dev/md127
        Version : 1.2
  Creation Time : Thu Sep  6 10:39:57 2012
     Raid Level : raid5
     Array Size : 8790402048 (8383.18 GiB 9001.37 GB)
  Used Dev Size : 2930134016 (2794.39 GiB 3000.46 GB)
   Raid Devices : 4
  Total Devices : 0
    Persistence : Superblock is persistent

    Update Time : Fri Sep  7 17:19:47 2012
          State : clean, FAILED
 Active Devices : 0
Working Devices : 0
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       0        0        1      removed
       2       0        0        2      removed
       3       0        0        3      removed

I’ve tried to do mdadm --stop /dev/md127 but:

mdadm --stop /dev/md127
mdadm: Cannot get exclusive access to /dev/md127:Perhaps a running process, mounted filesystem or active volume group?

I made sure that it’s unmounted, umount -l /dev/md127 and confirmed that it indeed is unmounted:

umount /dev/md127
umount: /dev/md127: not mounted

I’ve tried to zero superblock of each drive and I get (for each drive):

mdadm --zero-superblock /dev/sde1
mdadm: Unrecognised md component device - /dev/sde1

Here's output of lsof | grep md127:

lsof|grep md127
md127_rai  276       root  cwd       DIR                9,0          4096          2 /
md127_rai  276       root  rtd       DIR                9,0          4096          2 /
md127_rai  276       root  txt   unknown                                             /proc/276/exe

What else can I do? LVM is not even installed so it can't be a factor.

After much poking around I finally found what was preventing me from stoping the array. It was SAMBA process. After service smbd stop I was able to stop the array. It’s strange though because although the array was mounted and shared via SAMBA at one point in time, when I tried to stop it it was already unmounted.

share|improve this question
At this point, I think it's safe to use the --force option if you haven't tried it already. Also, what is process 276 on your system? [mdadm] ? – Darth Android Sep 7 '12 at 15:38
It doesn't work, I get the same message: "mdadm: Cannot get exclusive access to /dev/md127:Perhaps a running process, mounted filesystem or active volume group?" – matt Sep 7 '12 at 20:51
sudo fuser -vm /dev/md127 might show what process has a handle on the array. – Nick Sandor Aug 3 '13 at 15:13

I realize that this is an old question and the original poster believed that SAMBA was the issue, but I experienced the same exact problem and think that very likely the issue was not SAMBA (I actually don’t even have SAMBA), since it didn’t show up in the lsof output, but rather the user was already in the RAID mount-point directory when they switched to root or did a sudo.

In my case, the problem was that I started my root shell when my regular user was in a directory located on that mounted /dev/md127 drive.

user1@comp1:/mnt/md127_content/something$ su -
root@comp1:~# umount /dev/md127
umount: /dev/md127: target is busy

Here is the output of lsof in my case:

root@comp1:root@comp1:~# lsof | grep /dev/md127
md127_rai  145            root  cwd       DIR      253,0     4096          2 /
md127_rai  145            root  rtd       DIR      253,0     4096          2 /
md127_rai  145            root  txt   unknown                                /proc/145/exe

Even though lsof | grep md125 didn’t show any processes except [md127_raid1], I could not unmount /dev/md127. And while umount -l /dev/md127 does hide /dev/md127 from the output of mount, the drive is apparently still busy, and when mdadm --stop /dev/md127 is attempted, the same error is shown:

mdadm: Cannot get exclusive access to /dev/md127:Perhaps a running process, mounted filesystem or active volume group?

SOLUTION is simple: check if there are any users logged in who are still in a directory on that drive. Especially, check if the root shell you are using was started when your regular user's current directory was on that drive. Switch to that users shell (maybe just exit your root shall), move somewhere else, and umount and mdadm --stop will work:

root@comp1:~# exit
user1@comp1:/mnt/md127_content/something$ cd /
user1@comp1:/$ su -
root@comp1:~# umount /dev/md127
root@comp1:~# mdadm --stop /dev/md127
mdadm: stopped /dev/md127
share|improve this answer
@sd1074 You might be on something, but I'm not sure if my issue was caused by spawning root shell from the path in question - I would have to stop the samba service, exit the root shell, change directory as regular user, start root shell again and only then stop the array. Which is possible, but not likely. I think that acceptable answer should show how to determine which process is blocking mdadm array from stopping. lsof clearly fails here for some reason. – matt Dec 17 '15 at 22:06
@sd1074 If you have reproducible test case could you check if any of devices used as mdadm array component have open files reported by lsof? ( You need to compare numbers reported by lsof in DEVICE column against minor/major numbers of those devices). – matt Dec 17 '15 at 22:17
@matt, I kept the log of my adventures with that raid. I added the output of lsof to my answer. – sd1074 Dec 18 '15 at 2:39
@matt Kudos for coming back to this question nearly 3 years later! – JakeGould Dec 18 '15 at 3:17

I was running into similar issues but I didn't have the raid device mounted in any way. Stopping SAMBA didn't seem to help either. lsof showed nothing.

Everything just resulted in:

# mdadm --stop /dev/md2
mdadm: Cannot get exclusive access to /dev/md2:Perhaps a running process, mounted filesystem or active volume group?

What finally fixed it for me was remembering that this was a swap partition - so I just had to swapoff /dev/md2 - this allowed me to mdadm --stop /dev/md2 successfully.

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