df used versus available

ransomshell

Did I do something wrong here:

hilljack@brr10:~$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 3.9G 0 3.9G 0% /dev
tmpfs 791M 584K 790M 1% /run
/dev/vda3 125G 13G 113G 11% /
tmpfs 3.9G 0 3.9G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
/dev/vda2 121M 142K 120M 1% /boot/efi
/dev/vdb1 9.7T 132G 9.1T 2% /storage
tmpfs 791M 0 791M 0% /run/user/1000

Why is Avail for /dev/vdb1 600G less than Size but Used is only 132G?

Hundreds of 50MB files (Synology Hyper Backup files), 4K blocks on ext4.

hilljack@brr10:~$ du /storage/ -h
4.0K /storage/synology
16K /storage/lost+found
2.8G /storage/tmp
129G /storage/rclone_backup
4.0K /storage/rclone
132G /storage/

darkimmortal

tune2fs -m 0 /dev/vdb1

ransomshell

@darkimmortal said:
tune2fs -m 0 /dev/vdb1

Well hell, that was easy. Today I learned about reserved space.

Thanks a bunch!