On 19/08/12 14:15, Hugo Mills wrote:

On Sun, Aug 19, 2012 at 02:08:17PM +0000, Daniel Pocock wrote:

quoted

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?

Here is the package version I have:

# dpkg --list | grep btrfs
ii  btrfs-tools                           0.19+20120328-7
       Checksumming Copy on Write Filesystem utilities

Here is a more thorough dmesg, since boot, does this suggest the scan
was invoked?  I remember seeing some message about checking for btrfs
filesystems just after selecting the kernel in grub (root is ext3)


# dmesg | grep btrfs
[   40.677505] btrfs: setting nodatacow
[   40.677514] btrfs: turning off barriers
[17216.145092] device fsid c959d4a5-0713-4685-b572-8a679ec37e20 devid 1
transid 34 /dev/mapper/vg00-btrfsvol0_0
[17216.145639] btrfs: disk space caching is enabled
[17216.146987] btrfs: failed to read the system array on dm-100
[17216.147556] btrfs: open_ctree failed
[17310.978518] device fsid c959d4a5-0713-4685-b572-8a679ec37e20 devid 1
transid 34 /dev/mapper/vg00-btrfsvol0_0
[17310.993882] btrfs: disk space caching is enabled
[17598.736657] device fsid c959d4a5-0713-4685-b572-8a679ec37e20 devid 1
transid 37 /dev/mapper/vg00-btrfsvol0_0
[17598.750849] btrfs: disk space caching is enabled

quoted

Then I did btrfsck - it reported no errors, but mounted OK:

# btrfsck /dev/mapper/vg00-btrfsvol0_0

[...]

   The first thing that btrfsck does is to do a device scan.

[...]

Ok, that is most likely why my next mount attempted succeeded