Re: fail to mount after first reboot

[Daniel Pocock <daniel@pocock.com.au>]

On 19/08/12 18:02, Daniel Pocock wrote:
> 
> 
> On 19/08/12 16:51, Hugo Mills wrote:
>> On Sun, Aug 19, 2012 at 02:33:14PM +0000, Daniel Pocock wrote:
>>> On 19/08/12 14:15, Hugo Mills wrote:
>>>> On Sun, Aug 19, 2012 at 02:08:17PM +0000, Daniel Pocock wrote:
>>>>> I created a 1TB RAID1.  So far it is just for testing, no important data
>>>>> on there.
>>>>>
>>>>> After a reboot, I tried to mount it again
>>>>>
>>>>> # mount /dev/mapper/vg00-btrfsvol0_0 /mnt/btrfs0
>>>>> mount: wrong fs type, bad option, bad superblock on
>>>>> /dev/mapper/vg00-btrfsvol0_0,
>>>>>        missing codepage or helper program, or other error
>>>>>        In some cases useful info is found in syslog - try
>>>>>        dmesg | tail  or so
>>>>
>>>>    With multi-volume btrfs filesystems, you have to run "btrfs dev
>>>> scan" before trying to mount it. Usually, the distribution will do
>>>> this in the initrd (if you've installed its btrfs-progs package).
>>>
>>> I'm running Debian, I've just updated the system from squeeze to wheezy
>>> (with 3.2 kernel) so I could try btrfs and do other QA testing on wheezy
>>> (as it is in the beta phase now)
>>>
>>> I already had the btrfs-tools package installed, before creating the
>>> filesystem.  So it appears Debian doesn't have an init script
>>>
>>> It does have /lib/udev/rules.d/60-btrfs.rules:
>>> SUBSYSTEM!="block", GOTO="btrfs_end"
>>> ACTION!="add|change", GOTO="btrfs_end"
>>> ENV{ID_FS_TYPE}!="btrfs", GOTO="btrfs_end"
>>> RUN+="/sbin/modprobe btrfs"
>>> RUN+="/sbin/btrfs device scan $env{DEVNAME}"
>>>
>>> LABEL="btrfs_end"
>>>
>>> but I'm guessing that isn't any use to my logical volumes that are
>>> activated early in the boot sequence?
>>>
>>> Could I be having this problem because I put my btrfs on logical volumes?
>>
>>    Possibly. You may need the "Device mapper uevents" option in the
>> kernel (CONFIG_DM_UEVENT) to trigger that udev rule when you enable
>> your VG(s). Not sure if it's available/enabled in your kernel.
>>
> 
> I've created a Debian bug report for the issue:
> 
>   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=685311
> 
> Thanks for the quick feedback about this


Just a quick update, the Debian bug report now includes a udev rule that
makes the scan happen automatically, if anyone can suggest an even
better way of doing this it would be really helpful:

cat > /lib/udev/rules.d/99-btrfs.rules << EOF
SUBSYSTEM!="block", GOTO="btrfs_lvm_end"
ENV{DM_UUID}!="LVM-?*", GOTO="btrfs_lvm_end"
RUN+="/sbin/modprobe btrfs"
RUN+="/sbin/btrfs device scan $env{DEVNAME}"

LABEL="btrfs_lvm_end"
EOF