Degraded volume silently fails to mount

Degraded volume silently fails to mount

[Michael Tharp]

Hi list,

I've got a 4 disk raid1 volume that has one failed disk. I have so far 
been unable to mount it in degraded mode, but the failure is that 
"mount" silently does nothing.

  # btrfs fi sh
warning devid 2 not found already
Label: 'seneca'  uuid: b9da07f5-c0fd-45ad-861b-d1bcad6cbf4c
	Total devices 4 FS bytes used 581.71GiB
	devid    1 size 931.51GiB used 334.02GiB path /dev/mapper/luks-seneca-1
	devid    3 size 931.51GiB used 334.01GiB path /dev/mapper/luks-seneca-3
	devid    4 size 931.51GiB used 334.01GiB path /dev/mapper/luks-seneca-4
	*** Some devices missing

Btrfs v3.18.1
  # mount -t btrfs -o degraded /dev/mapper/luks-seneca-1 /seneca
  # echo $?
0
  # ls /seneca/
  # grep seneca /proc/mounts
  # dmesg |tail
[   84.955467] BTRFS: device label seneca devid 1 transid 1753 /dev/dm-4
[   87.926347] BTRFS: device label seneca devid 4 transid 1753 /dev/dm-5
[  107.069109] BTRFS: device label seneca devid 3 transid 1753 /dev/dm-6
[  195.267046] BTRFS info (device dm-6): allowing degraded mounts
[  195.267094] BTRFS info (device dm-6): disk space caching is enabled
[  195.267133] BTRFS: has skinny extents
[  195.277615] BTRFS warning (device dm-6): devid 2 missing
[  781.160250] BTRFS info (device dm-6): allowing degraded mounts
[  781.160270] BTRFS info (device dm-6): disk space caching is enabled
[  781.160286] BTRFS: has skinny extents
  # uname -a
Linux ambrosia.homeslice 3.19.3-200.fc21.x86_64 #1 SMP Thu Mar 26 
21:39:42 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
  # btrfs --version
Btrfs v3.18.1


Any ideas?

Re: Degraded volume silently fails to mount

[Hugo Mills]

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On Mon, Apr 13, 2015 at 09:51:09AM -0400, Michael Tharp wrote:
> Hi list,
> 
> I've got a 4 disk raid1 volume that has one failed disk. I have so
> far been unable to mount it in degraded mode, but the failure is
> that "mount" silently does nothing.

   Check to see if systemd is unmounting it immediately after
mount. This seems to be the usual reason for silent failures to mount
an FS these days.

   Hugo.

>  # btrfs fi sh
> warning devid 2 not found already
> Label: 'seneca'  uuid: b9da07f5-c0fd-45ad-861b-d1bcad6cbf4c
> 	Total devices 4 FS bytes used 581.71GiB
> 	devid    1 size 931.51GiB used 334.02GiB path /dev/mapper/luks-seneca-1
> 	devid    3 size 931.51GiB used 334.01GiB path /dev/mapper/luks-seneca-3
> 	devid    4 size 931.51GiB used 334.01GiB path /dev/mapper/luks-seneca-4
> 	*** Some devices missing
> 
> Btrfs v3.18.1
>  # mount -t btrfs -o degraded /dev/mapper/luks-seneca-1 /seneca
>  # echo $?
> 0
>  # ls /seneca/
>  # grep seneca /proc/mounts
>  # dmesg |tail
> [   84.955467] BTRFS: device label seneca devid 1 transid 1753 /dev/dm-4
> [   87.926347] BTRFS: device label seneca devid 4 transid 1753 /dev/dm-5
> [  107.069109] BTRFS: device label seneca devid 3 transid 1753 /dev/dm-6
> [  195.267046] BTRFS info (device dm-6): allowing degraded mounts
> [  195.267094] BTRFS info (device dm-6): disk space caching is enabled
> [  195.267133] BTRFS: has skinny extents
> [  195.277615] BTRFS warning (device dm-6): devid 2 missing
> [  781.160250] BTRFS info (device dm-6): allowing degraded mounts
> [  781.160270] BTRFS info (device dm-6): disk space caching is enabled
> [  781.160286] BTRFS: has skinny extents
>  # uname -a
> Linux ambrosia.homeslice 3.19.3-200.fc21.x86_64 #1 SMP Thu Mar 26
> 21:39:42 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
>  # btrfs --version
> Btrfs v3.18.1
> 
> 
> Any ideas?

-- 
Hugo Mills             | What's a Nazgûl like you doing in a place like this?
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                                Illiad

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Re: Degraded volume silently fails to mount

[Michael Tharp]

On 4/13/2015 10:07, Hugo Mills wrote:
> On Mon, Apr 13, 2015 at 09:51:09AM -0400, Michael Tharp wrote:
>> Hi list,
>>
>> I've got a 4 disk raid1 volume that has one failed disk. I have so
>> far been unable to mount it in degraded mode, but the failure is
>> that "mount" silently does nothing.
>
>     Check to see if systemd is unmounting it immediately after
> mount. This seems to be the usual reason for silent failures to mount
> an FS these days.

Sigh, that was it. Thanks. Faith in btrfs restored.

I had a custom unit file because the generated ones weren't getting the 
LUKS device dependencies correct. When the drive failed I commented out 
the fstab and crypttab entries but forgot about the custom unit file.