After BTRFS devoured space on my / partition am watching it, and disk space a bit closer, scrubbing regularly appeared useful.
So usually start checking scrub status, then scrub start, then scrub status after enough time passes, when usually see completed OK.
Today, several attempts found btrfs scrub have aborted, not completing scrubs, how to learn why, and what (if anything) need do so scrub completes OK.
linux-7769:~ # btrfs device stats /dev/sda3
[/dev/sda3].write_io_errs 0
[/dev/sda3].read_io_errs 0
[/dev/sda3].flush_io_errs 0
[/dev/sda3].corruption_errs 0
[/dev/sda3].generation_errs 0
linux-7769:~ # btrfs scrub status /dev/sda3
scrub status for xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
scrub started at Tue Apr 28 07:20:16 2015 and was aborted after 37 seconds
total bytes scrubbed: 3.74GiB with 0 errors
linux-7769:~ # btrfs scrub start /dev/sda3
scrub started on /dev/sda3, fsid xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (pid=5413)
linux-7769:~ # btrfs scrub status /dev/sda3
scrub status for xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
scrub started at Tue Apr 28 08:15:36 2015 and was aborted after 38 seconds
total bytes scrubbed: 3.75GiB with 0 errors
linux-7769:~ # btrfs device stats /dev/sda3
[/dev/sda3].write_io_errs 0
[/dev/sda3].read_io_errs 0
[/dev/sda3].flush_io_errs 0
[/dev/sda3].corruption_errs 0
[/dev/sda3].generation_errs 0
linux-7769:~ # df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 41G 11G 29G 27% /
devtmpfs 3.7G 0 3.7G 0% /dev
tmpfs 3.7G 96K 3.7G 1% /dev/shm
tmpfs 3.7G 2.2M 3.7G 1% /run
tmpfs 3.7G 0 3.7G 0% /sys/fs/cgroup
/dev/sda3 41G 11G 29G 27% /.snapshots
/dev/sda3 41G 11G 29G 27% /var/tmp
/dev/sda3 41G 11G 29G 27% /var/spool
/dev/sda3 41G 11G 29G 27% /var/opt
/dev/sda3 41G 11G 29G 27% /var/log
/dev/sda3 41G 11G 29G 27% /var/lib/mailman
/dev/sda3 41G 11G 29G 27% /var/lib/pgsql
/dev/sda3 41G 11G 29G 27% /usr/local
/dev/sda3 41G 11G 29G 27% /var/crash
/dev/sda3 41G 11G 29G 27% /srv
/dev/sda3 41G 11G 29G 27% /var/lib/named
/dev/sda3 41G 11G 29G 27% /tmp
/dev/sda3 41G 11G 29G 27% /opt
/dev/sda3 41G 11G 29G 27% /boot/grub2/x86_64-efi
/dev/sda3 41G 11G 29G 27% /boot/grub2/i386-pc
/dev/sda4 424G 47G 378G 11% /home
linux-7769:~ #
linux-7769:~ # journalctl --all --since='2015-04-28 06:00' | grep -i 'btrfs'
Apr 28 06:40:35 linux-7769 kernel: Btrfs loaded, assert=on
Apr 28 06:40:35 linux-7769 kernel: BTRFS: device fsid xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx devid 1 transid 50569 /dev/sda3
Apr 28 06:40:35 linux-7769 systemd-fsck[298]: /sbin/fsck.btrfs: BTRFS file system.
Apr 28 06:40:35 linux-7769 kernel: BTRFS info (device sda3): disk space caching is enabled
Apr 28 06:40:38 linux-7769 kernel: BTRFS info (device sda3): disk space caching is enabled
linux-7769:~ #