$ sudo btrfs check -s 0 /dev/sda6
Opening filesystem to check...
Checking filesystem on /dev/sda6
UUID: 8fd7707b-9c79-43e0-bc5f-bee739946655
[1/7] checking root items
[2/7] checking extents
[3/7] checking free space cache
[4/7] checking fs roots
root 5 inode 18446744073709551605 errors 2001, no inode item, link count wrong
    unresolved ref dir 256 index 32 namelen 25 name System Volume Information filetype 2 errors 4, no inode ref
root 5 inode 18446744073709551606 errors 2000, link count wrong
    unresolved ref dir 18446744073709551605 index 2 namelen 14 name WPSettings.dat filetype 0 errors 3, no dir item, no dir index
root 5 inode 18446744073709551607 errors 2000, link count wrong
    unresolved ref dir 18446744073709551605 index 3 namelen 17 name IndexerVolumeGuid filetype 0 errors 3, no dir item, no dir index
ERROR: errors found in fs roots
found 22651777024 bytes used, error(s) found
total csum bytes: 21328972
total tree bytes: 600080384
total fs tree bytes: 535052288
total extent tree bytes: 36601856
btree space waste bytes: 93728326
file data blocks allocated: 23825588224
 referenced 26065018880