[hendry@nuc ~]$ sudo btrfs fi show /mnt/raid1/
Label: 'extraid1'  uuid: 5cab2a4a-e282-4931-b178-bec4c73cdf77
        Total devices 4 FS bytes used 1.82TiB
        devid    2 size 1.82TiB used 1.82TiB path /dev/sdb1
        devid    3 size 1.82TiB used 1.82TiB path /dev/sdc1
        devid    4 size 3.64TiB used 1.00GiB path /dev/sde1
        devid    5 size 3.64TiB used 1.00GiB path /dev/sdd1

[hendry@nuc ~]$ sudo btrfs fi usage /mnt/raid1/
Overall:
    Device size:                  10.92TiB
    Device allocated:              3.64TiB
    Device unallocated:            7.28TiB
    Device missing:                  0.00B
    Used:                          3.64TiB
    Free (estimated):              3.64TiB      (min: 3.64TiB)
    Data ratio:                       2.00
    Metadata ratio:                   2.00
    Global reserve:              512.00MiB      (used: 0.00B)

Data,RAID1: Size:1.81TiB, Used:1.81TiB
   /dev/sdb1       1.81TiB
   /dev/sdc1       1.81TiB
   /dev/sdd1       1.00GiB
   /dev/sde1       1.00GiB

Metadata,RAID1: Size:6.00GiB, Used:5.13GiB
   /dev/sdb1       6.00GiB
   /dev/sdc1       6.00GiB

System,RAID1: Size:32.00MiB, Used:288.00KiB
   /dev/sdb1      32.00MiB
   /dev/sdc1      32.00MiB

Unallocated:
   /dev/sdb1       1.02MiB
   /dev/sdc1       1.01MiB
   /dev/sdd1       3.64TiB
   /dev/sde1       3.64TiB
[hendry@nuc ~]$