By default, 5% of space on ext4 partitions is reserved. On large drives this can result in hundreds of gigabytes being wasted! If you are using ext4, make sure to run
sudo tune2fs -m 0 /dev/yourpartition.
I only realised this just now when looking at
df output and noticing that
Avail did not add up to
Size. By doing this on all my nodes I got over a terabyte of additional storage, for free.