btrfsck output: What does it all mean?

[Martin <m_btrfs@ml1.co.uk>]

This is the btrfsck output for a real-world rsync backup onto a btrfs
raid1 mirror across 4 drives (yes, I know at the moment for btrfs raid1
there's only ever two copies of the data...)


checking extents
checking fs roots
root 5 inode 18446744073709551604 errors 2000
root 5 inode 18446744073709551605 errors 1
root 256 inode 18446744073709551604 errors 2000
root 256 inode 18446744073709551605 errors 1
found 3183604633600 bytes used err is 1
total csum bytes: 3080472924
total tree bytes: 28427821056
total fs tree bytes: 23409475584
btree space waste bytes: 4698218231
file data blocks allocated: 3155176812544
 referenced 3155176812544
Btrfs Btrfs v0.19
Command exited with non-zero status 1


So: What does that little lot mean?

The drives were mounted and active during an unexpected power-plug pull :-(


Safe to mount again or are there other checks/fixes needed?

Thanks,
Martin