mdadm Device or resource busy not by dmraid

Question

I have an issue with a new mdadm raid.

When i try to:

root@dys:~# mdadm --add --verbose /dev/md0 /dev/sdb1
mdadm: Cannot open /dev/sdb1: Device or resource busy

dmraid i pointed as the usual problem but it's not even installed.

Also tried to check it with lsof and no result.

Im just out of ideeas

the output of /proc/mdstat if of any help:

root@dys:~# cat /proc/mdstat
Personalities : [raid1]
md1 : active (auto-read-only) raid1 sdb2[2] sda2[1]
      7858164 blocks super 1.2 [2/2] [UU]

md0 : active (auto-read-only) raid1 sda1[1]
      968900472 blocks super 1.2 [2/1] [_U]

unused devices: <none>

Solution

What about this way: mdadm /dev/md0 -a /dev/sdb1 ?

What is the output of lsblk /dev/sdb1?

Comments

[etagenklo]

Are you sure /dev/sdb1 is not mounted?

[Debrian]

mount | grep sdb1 doesn't show anything, and /dev/md0 on / type ext4 (rw,errors=remount-ro). Any other way to check ?

[Debrian]

Same result: mdadm /dev/md0 -a /dev/sdb1 mdadm: Cannot open /dev/sdb1: Device or resource busy

[poige]

@Adrian, ok, let's go further — see update

[Debrian]

Ok that helped a lot. First of all lsblk is not present in debian stable, so i had to get it from testing and discovered that /dev/sdb1 was mounted on /, although mount and umount where saying it's not. I redo the grub configuration (the first time i miss-copied a uuid it seems) and now everything works according to plan. Lesson learned lsblk is a nice tool.