"Invalid argument" when mounting a btrfs raid1 filesystem

[Christoph Groth <cwg@falma.de>]

Hello,

I'm trying to install current Debian testing (=kernel version 3.2) with
btrfs as the root file system.  There is also a small ext3 /boot
partition.

I create a btrfs raid1 file system with the command

mkfs.btrfs -d raid1 /dev/sda2 /dev/sdb2

Then I can mount it and finish the installation successfully.  Booting
doesn't work, however: initrd complains that it cannot mount /dev/sda2:
"Invalid argument".

The funny thing is, that in the initrd console I can mount /dev/sdb2!
So I changed the kernel parameter in grub.cfg to mount /dev/sdb2
instead, but the problem persists: Now I can mount /dev/sda2 in the
initrd console!

In fact, when I boot a rescue system from a thumbdrive, the same thing
happens:

# mount -t btrfs /dev/sda2 /mnt
mount: mounting /dev/sda2 on /mnt failed: Invalid argument
# mount -t btrfs /dev/sdb2 /mnt
#

When I keep trying to mount the same device, it keeps failing.  When I
start mounting /dev/sdb2, it works for /dev/sda2...

Isn't this very weird?  Any ideas?

thanks,
Christoph