Re: [dm-devel] Cannot mount underlying block device after creating dm device.

[Phillip Susi <psusi cfl rr com>]

On 11/2/2011 11:18 PM, Sanjana wrote:
> [root bladelinux01 ~]# mount /dev/loop0 /mnt/
> mount: /dev/loop0 already mounted or /mnt/ busy
> [root bladelinux01 ~]# mount /dev/loop1 /mnt/
> mount: /dev/loop1 already mounted or /mnt/ busy
>
> But if I remove the dm device created and try to mount the underlying
> block-device, I can mount both the device which took part in mirroring and
> I can access the data in both the disk.
> [root bladelinux01 ~]# dmsetup remove raid1
> [root bladelinux01 ~]# mount /dev/loop0 /mnt/
> [root bladelinux01 ~]# ls -l /mnt/
> total 51
> drwx------. 2 root root 12288 Nov  2 22:32 lost+found
> -rw-------. 1 root root 37417 Nov  2 22:38 messages
>
> [root bladelinux01 ~]# umount /mnt/
> [root bladelinux01 ~]# mount /dev/loop1 /mnt/
> [root bladelinux01 ~]# ls -l /mnt/
> total 51
> drwx------. 2 root root 12288 Nov  2 22:32 lost+found
> -rw-------. 1 root root 37417 Nov  2 22:38 messages
>
> Why is this behavior. any explanation, please....

Simple; the loop devices are still open by device-mapper, so mount is 
telling you they are busy.  Just because the raid device has zero opens 
does not mean that it closes the underlying devices.