You have an unmounted btrfs file system:
# btrfs filesystem show
Label: 'Btrfs' uuid: 7bfe3239-47ee-442b-b9f8-49f88b6b1be4
Total devices 3 FS bytes used 300.51MB
devid 2 size 4.88GB used 1.06GB path /dev/sdd
devid 1 size 4.88GB used 580.00GB path /dev/sdc
devid 3 size 4.88GB used 1.50GB path /dev/sdb
You have these mounted devices:
# df -h

You have a mount point for the btrfs file system:
# ls -all /btrfs
total 0
drwxr-xr-x. 1 root root 0 Aug 12 10:17 .
dr-xr-xr-x. 1 root root 276 Aug 12 10:36 ..
Examine these steps:
1 . Manual defragment is not needed. Btrfs will defragment it automatically.
2 . btrfs device defragment /dev/sdd
3 . btrfs filesystem defragment /btrfs
4 . btrfs device delete /dev/sdb /btrfs
5 . mount UUID=7bfe3239-47ee-442b-b9f8-49f88b6b1be4 /btrfs
6 . btrfs device delete /dev/sdb /dev/sdd
What is the correct order to delete the /dev/sdb device from the btrfs file system and for defragmenting the reduced file system?