Why is Used + Available disk space always less than Total disk space?
root@localhost:~ $ df /dev/sdb1
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdb1 1922858352 23247088 1801935664 2% /mnt/external/sdb1
used+available = 1825182752
Size - 1825182752 = 97675600
97675600 / 1825182752 = 5% this is the default reserved space for root user.