# btrfs fi sh
Label: 'media'  uuid: 4336541f-89f7-47f4-94bb-a99b987f4f94
        Total devices 4 FS bytes used 13.68TiB
        devid    1 size 10.91TiB used 9.15TiB path /dev/sdx
        devid    2 size 10.91TiB used 9.15TiB path /dev/sdy
        devid    3 size 7.28TiB used 5.52TiB path /dev/sdu
        devid    4 size 0 used 0 path /dev/sdw MISSING
        
Label: 'local-btrfs'  uuid: c0b4bd00-3afa-43fd-bd3d-c8f73df12df0
        Total devices 8 FS bytes used 144.00KiB
        devid    1 size 558.79GiB used 88.26GiB path /dev/sdn
        devid    2 size 558.79GiB used 88.26GiB path /dev/sdo
        devid    3 size 558.79GiB used 88.26GiB path /dev/sdp
        devid    4 size 558.79GiB used 88.26GiB path /dev/sdq
        devid    5 size 558.79GiB used 88.00GiB path /dev/sdr
        devid    6 size 558.79GiB used 88.00GiB path /dev/sds
        devid    7 size 558.79GiB used 88.00GiB path /dev/sdt
        devid    9 size 558.79GiB used 88.00GiB path /dev/sdv

# btrfs device scan
Scanning for Btrfs filesystems
registered: /dev/sdy
registered: /dev/sdo
registered: /dev/sdu
registered: /dev/sds
registered: /dev/sdq
registered: /dev/sdx
registered: /dev/sdn
registered: /dev/sdv
registered: /dev/sdt
registered: /dev/sdr
registered: /dev/sdp
registered: /dev/sdaj
ERROR: device scan failed on '/dev/sdaj': File exists
ERROR: there were 1 errors while registering devices

# btrfs fi u /mnt/media
Overall:
    Device size:                  36.38TiB
    Device allocated:             27.50TiB
    Device unallocated:            8.88TiB
    Device missing:                7.28TiB
    Device slack:                    0.00B
    Used:                         27.37TiB
    Free (estimated):              4.51TiB      (min: 4.51TiB)
    Free (statfs, df):             3.59TiB
    Data ratio:                       2.00
    Metadata ratio:                   2.00
    Global reserve:              512.00MiB      (used: 0.00B)
    Multiple profiles:                  no

Data,RAID1: Size:13.74TiB, Used:13.67TiB (99.50%)
   /dev/sdx        9.14TiB
   /dev/sdy        9.14TiB
   /dev/sdu        5.51TiB
   /dev/sdw        3.67TiB

Metadata,RAID1: Size:15.00GiB, Used:14.77GiB (98.47%)
   /dev/sdx       10.00GiB
   /dev/sdy       10.00GiB
   /dev/sdu        6.00GiB
   /dev/sdw        4.00GiB

System,RAID1: Size:32.00MiB, Used:2.00MiB (6.25%)
   /dev/sdx       32.00MiB
   /dev/sdy       32.00MiB

Unallocated:
   /dev/sdx        1.76TiB
   /dev/sdy        1.76TiB
   /dev/sdu        1.76TiB
   /dev/sdw        3.60TiB

# dmesg
...
[7425634.222974] kworker/u130:6: attempt to access beyond end of device
                 sdw: rw=1052673, sector=4509755520, nr_sectors = 32 limit=0
[7425634.226063] BTRFS error (device sdx): bdev /dev/sdw errs: wr 16, rd 0, flush 0, corrupt 0, gen 0
[7425634.227983] kworker/u130:6: attempt to access beyond end of device
                 sdw: rw=1052673, sector=4509759360, nr_sectors = 32 limit=0
[7425634.231168] BTRFS error (device sdx): bdev /dev/sdw errs: wr 17, rd 0, flush 0, corrupt 0, gen 0