2012-12-20.

Am using BTRFS in a few places, one of them the root 
filesystem on the OpenSuSE 12.2 system on the desktop
at home.

An initial annoyance was that it automatically activated
snapshots, which accumulated quickly and filled the disk.
To add to the trouble, the normal tools (e.g. df) don't 
see this as a full disk, as the space under .snapshots 
isn't declared as disk useage.

The btrfs command can list and change these sorts of things.

# df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        25G   16G  7.9G  67% /

# grep sda3 /etc/mtab                    
/dev/sda3 / btrfs rw,relatime,ssd,space_cache 0 0

# btrfs filesystem show
failed to read /dev/sr0
Label: none  uuid: 8c3f8981-ebf8-4a80-a20d-881f13ab2bf1
        Total devices 1 FS bytes used 14.93GB
        devid    1 size 25.00GB used 25.00GB path /dev/sda3
Btrfs v0.19+

# btrfs filesystem df / 
Data: total=21.97GB, used=14.10GB
System, DUP: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=1.50GB, used=856.25MB
Metadata: total=8.00MB, used=0.00

# btrfs scrub start /

t.b.c