I have an openSUSE 12.1 install on my main desktop running with btrfs filesystem for root (/boot is ext4). I started having issues today with KDE informing me that disk space is almost all gone and eventually it decided it was gone and crashed my desktop.
I used Alt+F1 to switch to a terminal screen and although I was sure I was no where near the 1TB limit of my hard disk I moved some 150/200GB of music and video files onto an external drive and rebooted. Didn't help, same problem, same crash.
Once more I switched to a terminal screen and used du to confirm that I had indeed only used about half of my total diskspace but df (including the btrfs-progs version) insists I have used 100% of available diskspace and so my desktop crashes each and every time I log in.
Using the btrfs defrag utility doesn't help either. As such I am at a bit of a loss as to where to go next.