I have btrfs raid-1. When one of the drives failed, I ran out of disk space.
The disk was used by:
* /var/log/messages
* /var/log/kern.log
* /var/log/syslog
All of these contained errors that look like this:
```
Mar 31 15:15:55 b2 kernel: [ 3816.592556] BTRFS warning (device
mmcblk0p4): i/o error at logical 217488986112 on dev /dev/sda,
physical 182894366720, root 5, inode 2943, offset 18087936, length
4096, links 1 (path: bitcoin/bitcoin-data/blocks/rev00740.dat)
Mar 31 15:15:55 b2 kernel: [ 3816.604975] scrub_handle_errored_block:
7743 callbacks suppressed
Mar 31 15:15:55 b2 kernel: [ 3816.604996] BTRFS error (device
mmcblk0p4): unable to fixup (regular) error at logical 217488797696 on
dev /dev/sda
```
also
```
Mar 31 15:20:45 b2 kernel: [ 4107.205771]
btrfs_dev_stat_print_on_error: 28954 callbacks suppressed
Mar 31 15:20:45 b2 kernel: [ 4107.205792] BTRFS error (device
mmcblk0p4): bdev /dev/sda errs: wr 1087192, rd 543622, flush 2,
corrupt 0, gen 0
Mar 31 15:20:45 b2 kernel: [ 4107.206125] BTRFS error (device
mmcblk0p4): bdev /dev/sda errs: wr 1087193, rd 543622, flush 2,
corrupt 0, gen 0
Mar 31 15:20:45 b2 kernel: [ 4107.206155] BTRFS error (device
mmcblk0p4): bdev /dev/sda errs: wr 1087194, rd 543622, flush 2,
corrupt 0, gen 0
Mar 31 15:20:45 b2 kernel: [ 4107.206165] scrub_handle_errored_block:
9645 callbacks suppressed
```
I have Linux l2 4.19.25+ #1205 Mon Feb 25 17:52:12 GMT 2019 armv6l GNU/Linux
btrfs-progs v4.7.3
$ btrfs fi show
Label: 'bitcoind' uuid: 8848dbdc-bf70-4de0-b06f-312ce71b396a
Total devices 2 FS bytes used 203.44GiB
devid 1 size 225.00GiB used 206.03GiB path /dev/sda
devid 2 size 225.00GiB used 206.03GiB path /dev/mmcblk0p4
$ btrfs fi df /mnt/btrfs_bitcoind/
Data, RAID1: total=204.00GiB, used=202.88GiB
System, RAID1: total=32.00MiB, used=48.00KiB
Metadata, RAID1: total=2.00GiB, used=581.30MiB
GlobalReserve, single: total=421.27MiB, used=0.00B
Alex
