How does one undelete or repair BTRFS partitions?

Question

Had a power‐cut last week and thought nothing of it but today when I opened (mounted) a data partition for archiving edited video files, I noticed it had 50GB free when it previously had only 2…

john@joran ~ > df -h /media/editing/
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda10      232G  181G   49G  79% /media/editing

john@joran ~ > sudo btrfs fi show /dev/sda10
Label: 'editing'  uuid: *snip*
    Total devices 1 FS bytes used 180.01GB
    devid    1 size 231.27GB used 229.54GB path /dev/sda10

john@joran ~ > sudo fsck.btrfs --repair /dev/sda10
found 193283719168 bytes used err is 0
total csum bytes: 188503800
total tree bytes: 255827968
total fs tree bytes: 1744896
btree space waste bytes: 49940305
file data blocks allocated: 1728409796608
 referenced 192990859264
Btrfs Btrfs v0.19

john@joran ~ > uname -a
*snip* 3.2.0-25-generic #40-Ubuntu SMP Wed May 23 20:30:51 UTC 2012 x86_64 GNU/Linux

Any advice?

Answer 1

Figure out what files are missing ( if any -- the free space simply may have been wrong before ), and restore them from backup.

If you don't have a backup, then sooner or later you are going to lose your data, especially if you store it on an experimental filesystem like btrfs.