root@raspberrypi:~# /usr/local/bin/btrfs-scrub.sh
root: Quick Metadata and Data Balance of /srv/dev-disk-by-label-BTRFS_LINEAR (/dev/sda)
Done, had to relocate 0 out of 6 chunks
Done, had to relocate 3 out of 6 chunks
Done, had to relocate 0 out of 5 chunks
Done, had to relocate 2 out of 5 chunks
root: Starting scrub of /srv/dev-disk-by-label-BTRFS_LINEAR
btrfs scrub start -Bd /srv/dev-disk-by-label-BTRFS_LINEAR
scrub device /dev/sda (id 1) done
	scrub started at Fri Nov 24 19:17:59 2017 and finished after 14 seconds
	total bytes scrubbed: 409.93MiB with 0 errors
scrub device /dev/sdb (id 2) done
	scrub started at Fri Nov 24 19:17:59 2017 and finished after 1 seconds
	total bytes scrubbed: 1008.00KiB with 65 errors
	error details: read=63 super=2
	corrected errors: 0, uncorrectable errors: 63, unverified errors: 0
ERROR: There are uncorrectable errors.



Corresponding dmesg output:
[ 4367.221650] usb 1-1.5: USB disconnect, device number 5
[ 4390.951356] BTRFS error (device sdb): bdev /dev/sdb errs: wr 1, rd 0, flush 0, corrupt 0, gen 0
[ 4390.951589] BTRFS error (device sdb): bdev /dev/sdb errs: wr 2, rd 0, flush 0, corrupt 0, gen 0
[ 4390.954913] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4390.954928] BTRFS error (device sdb): bdev /dev/sdb errs: wr 3, rd 0, flush 0, corrupt 0, gen 0
[ 4390.954980] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4390.954990] BTRFS error (device sdb): bdev /dev/sdb errs: wr 4, rd 0, flush 0, corrupt 0, gen 0
[ 4391.009290] BTRFS error (device sdb): bdev /dev/sdb errs: wr 5, rd 0, flush 0, corrupt 0, gen 0
[ 4391.009546] BTRFS error (device sdb): bdev /dev/sdb errs: wr 6, rd 0, flush 0, corrupt 0, gen 0
[ 4391.009560] BTRFS error (device sdb): bdev /dev/sdb errs: wr 7, rd 0, flush 0, corrupt 0, gen 0
[ 4391.013343] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.013357] BTRFS error (device sdb): bdev /dev/sdb errs: wr 8, rd 0, flush 0, corrupt 0, gen 0
[ 4391.013398] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.013409] BTRFS error (device sdb): bdev /dev/sdb errs: wr 9, rd 0, flush 0, corrupt 0, gen 0
[ 4391.064039] BTRFS error (device sdb): bdev /dev/sdb errs: wr 10, rd 0, flush 0, corrupt 0, gen 0
[ 4391.075123] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.075147] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.077296] BTRFS info (device sdb): relocating block group 14088667136 flags 20
[ 4391.172962] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.172986] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.455266] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.455290] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4391.516778] BTRFS info (device sdb): found 40 extents
[ 4391.616568] BTRFS info (device sdb): relocating block group 10867441664 flags 20
[ 4391.950766] BTRFS info (device sdb): found 64 extents
[ 4392.050030] BTRFS info (device sdb): relocating block group 10833887232 flags 18
[ 4392.170959] BTRFS info (device sdb): found 1 extents
[ 4392.476472] BTRFS info (device sdb): relocating block group 13014925312 flags 1
[ 4397.807061] btrfs_dev_stat_print_on_error: 154 callbacks suppressed
[ 4397.807071] BTRFS error (device sdb): bdev /dev/sdb errs: wr 165, rd 0, flush 0, corrupt 0, gen 0
[ 4397.807587] BTRFS error (device sdb): bdev /dev/sdb errs: wr 166, rd 0, flush 0, corrupt 0, gen 0
[ 4397.807611] BTRFS error (device sdb): bdev /dev/sdb errs: wr 167, rd 0, flush 0, corrupt 0, gen 0
[ 4397.820484] btrfs_end_buffer_write_sync: 42 callbacks suppressed
[ 4397.820504] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4397.820511] BTRFS error (device sdb): bdev /dev/sdb errs: wr 168, rd 0, flush 0, corrupt 0, gen 0
[ 4397.820532] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4397.820537] BTRFS error (device sdb): bdev /dev/sdb errs: wr 169, rd 0, flush 0, corrupt 0, gen 0
[ 4397.867630] BTRFS error (device sdb): bdev /dev/sdb errs: wr 170, rd 0, flush 0, corrupt 0, gen 0
[ 4397.867879] BTRFS error (device sdb): bdev /dev/sdb errs: wr 171, rd 0, flush 0, corrupt 0, gen 0
[ 4397.867953] BTRFS error (device sdb): bdev /dev/sdb errs: wr 172, rd 0, flush 0, corrupt 0, gen 0
[ 4397.871591] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4397.871598] BTRFS error (device sdb): bdev /dev/sdb errs: wr 173, rd 0, flush 0, corrupt 0, gen 0
[ 4397.871617] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4397.871623] BTRFS error (device sdb): bdev /dev/sdb errs: wr 174, rd 0, flush 0, corrupt 0, gen 0
[ 4397.873526] BTRFS info (device sdb): found 9 extents
[ 4403.230259] BTRFS error (device sdb): bdev /dev/sdb errs: wr 175, rd 0, flush 0, corrupt 0, gen 0
[ 4403.230493] BTRFS error (device sdb): bdev /dev/sdb errs: wr 176, rd 0, flush 0, corrupt 0, gen 0
[ 4403.230749] BTRFS error (device sdb): bdev /dev/sdb errs: wr 177, rd 0, flush 0, corrupt 0, gen 0
[ 4403.231007] BTRFS error (device sdb): bdev /dev/sdb errs: wr 178, rd 0, flush 0, corrupt 0, gen 0
[ 4403.231266] BTRFS error (device sdb): bdev /dev/sdb errs: wr 179, rd 0, flush 0, corrupt 0, gen 0
[ 4403.231462] BTRFS error (device sdb): bdev /dev/sdb errs: wr 180, rd 0, flush 0, corrupt 0, gen 0
[ 4403.241505] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.241513] BTRFS error (device sdb): bdev /dev/sdb errs: wr 181, rd 0, flush 0, corrupt 0, gen 0
[ 4403.241533] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.241538] BTRFS error (device sdb): bdev /dev/sdb errs: wr 182, rd 0, flush 0, corrupt 0, gen 0
[ 4403.287381] BTRFS error (device sdb): bdev /dev/sdb errs: wr 183, rd 0, flush 0, corrupt 0, gen 0
[ 4403.287533] BTRFS error (device sdb): bdev /dev/sdb errs: wr 184, rd 0, flush 0, corrupt 0, gen 0
[ 4403.291987] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.292008] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.350866] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.350889] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.352038] BTRFS info (device sdb): found 9 extents
[ 4403.382690] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.382713] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.414601] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.414623] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4403.449203] BTRFS info (device sdb): relocating block group 8652849152 flags 1
[ 4405.865831] BTRFS info (device sdb): found 17 extents
[ 4408.225853] BTRFS info (device sdb): found 17 extents
[ 4408.260762] btrfs_dev_stat_print_on_error: 60 callbacks suppressed
[ 4408.260771] BTRFS error (device sdb): bdev /dev/sdb errs: wr 245, rd 0, flush 0, corrupt 0, gen 0
[ 4408.261028] BTRFS error (device sdb): bdev /dev/sdb errs: wr 246, rd 0, flush 0, corrupt 0, gen 0
[ 4408.261157] BTRFS error (device sdb): bdev /dev/sdb errs: wr 247, rd 0, flush 0, corrupt 0, gen 0
[ 4408.264668] btrfs_end_buffer_write_sync: 14 callbacks suppressed
[ 4408.264673] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.264681] BTRFS error (device sdb): bdev /dev/sdb errs: wr 248, rd 0, flush 0, corrupt 0, gen 0
[ 4408.264700] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.264705] BTRFS error (device sdb): bdev /dev/sdb errs: wr 249, rd 0, flush 0, corrupt 0, gen 0
[ 4408.293342] BTRFS error (device sdb): bdev /dev/sdb errs: wr 250, rd 0, flush 0, corrupt 0, gen 0
[ 4408.293595] BTRFS error (device sdb): bdev /dev/sdb errs: wr 251, rd 0, flush 0, corrupt 0, gen 0
[ 4408.293648] BTRFS error (device sdb): bdev /dev/sdb errs: wr 252, rd 0, flush 0, corrupt 0, gen 0
[ 4408.296807] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.296815] BTRFS error (device sdb): bdev /dev/sdb errs: wr 253, rd 0, flush 0, corrupt 0, gen 0
[ 4408.296834] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.296839] BTRFS error (device sdb): bdev /dev/sdb errs: wr 254, rd 0, flush 0, corrupt 0, gen 0
[ 4408.336471] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.336494] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.385359] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.385382] BTRFS warning (device sdb): lost page write due to IO error on /dev/sdb
[ 4408.525121] BTRFS warning (device sdb): i/o error at logical 15162425344 on dev /dev/sdb, sector 2099232: metadata leaf (level 0) in tree 3
[ 4408.525129] BTRFS warning (device sdb): i/o error at logical 15162425344 on dev /dev/sdb, sector 2099232: metadata leaf (level 0) in tree 3
[ 4408.594206] BTRFS error (device sdb): unable to fixup (regular) error at logical 15162425344 on dev /dev/sdb
[ 4408.594629] BTRFS warning (device sdb): i/o error at logical 14088732672 on dev /dev/sdb, sector 4343936: metadata leaf (level 0) in tree 9
[ 4408.594635] BTRFS warning (device sdb): i/o error at logical 14088732672 on dev /dev/sdb, sector 4343936: metadata leaf (level 0) in tree 9
[ 4408.595860] BTRFS warning (device sdb): i/o error at logical 14088912896 on dev /dev/sdb, sector 4344288: metadata leaf (level 0) in tree 7
[ 4408.595866] BTRFS warning (device sdb): i/o error at logical 14088912896 on dev /dev/sdb, sector 4344288: metadata leaf (level 0) in tree 7
[ 4408.595937] BTRFS warning (device sdb): i/o error at logical 14088962048 on dev /dev/sdb, sector 4344384: metadata leaf (level 0) in tree 7
[ 4408.595942] BTRFS warning (device sdb): i/o error at logical 14088962048 on dev /dev/sdb, sector 4344384: metadata leaf (level 0) in tree 7
[ 4408.595953] BTRFS warning (device sdb): i/o error at logical 14089125888 on dev /dev/sdb, sector 4344704: metadata leaf (level 0) in tree 5
[ 4408.595959] BTRFS warning (device sdb): i/o error at logical 14089125888 on dev /dev/sdb, sector 4344704: metadata leaf (level 0) in tree 5
[ 4408.596108] BTRFS warning (device sdb): i/o error at logical 14089224192 on dev /dev/sdb, sector 4344896: metadata leaf (level 0) in tree 5
[ 4408.596114] BTRFS warning (device sdb): i/o error at logical 14089224192 on dev /dev/sdb, sector 4344896: metadata leaf (level 0) in tree 5
[ 4408.596199] BTRFS warning (device sdb): i/o error at logical 14089420800 on dev /dev/sdb, sector 4345280: metadata leaf (level 0) in tree 5
[ 4408.596205] BTRFS warning (device sdb): i/o error at logical 14089420800 on dev /dev/sdb, sector 4345280: metadata leaf (level 0) in tree 5
[ 4408.607196] BTRFS error (device sdb): unable to fixup (regular) error at logical 14088912896 on dev /dev/sdb
[ 4408.607286] BTRFS warning (device sdb): i/o error at logical 14089502720 on dev /dev/sdb, sector 4345440: metadata leaf (level 0) in tree 5
[ 4408.607292] BTRFS warning (device sdb): i/o error at logical 14089502720 on dev /dev/sdb, sector 4345440: metadata leaf (level 0) in tree 5
[ 4408.626320] BTRFS error (device sdb): unable to fixup (regular) error at logical 14088732672 on dev /dev/sdb
[ 4408.626400] BTRFS warning (device sdb): i/o error at logical 14089551872 on dev /dev/sdb, sector 4345536: metadata leaf (level 0) in tree 5
[ 4408.626405] BTRFS warning (device sdb): i/o error at logical 14089551872 on dev /dev/sdb, sector 4345536: metadata leaf (level 0) in tree 5
[ 4408.626560] BTRFS error (device sdb): unable to fixup (regular) error at logical 14088962048 on dev /dev/sdb
[ 4408.626608] BTRFS warning (device sdb): i/o error at logical 14088978432 on dev /dev/sdb, sector 4344416: metadata leaf (level 0) in tree 5
[ 4408.626613] BTRFS warning (device sdb): i/o error at logical 14088978432 on dev /dev/sdb, sector 4344416: metadata leaf (level 0) in tree 5
[ 4408.626945] BTRFS error (device sdb): unable to fixup (regular) error at logical 14089125888 on dev /dev/sdb
[ 4408.632489] BTRFS error (device sdb): unable to fixup (regular) error at logical 14089551872 on dev /dev/sdb
[ 4408.632687] BTRFS error (device sdb): unable to fixup (regular) error at logical 14088978432 on dev /dev/sdb
[ 4408.633046] BTRFS error (device sdb): unable to fixup (regular) error at logical 14089650176 on dev /dev/sdb
[ 4408.635422] BTRFS error (device sdb): unable to fixup (regular) error at logical 14089568256 on dev /dev/sdb
[ 4408.635637] BTRFS error (device sdb): unable to fixup (regular) error at logical 14088994816 on dev /dev/sdb