ext4 filesystem
df -h /dev/sda1
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 938G 72M 891G 1% /mnt/media
As you can see, the partition is 938 GB in size (1 TB SSD), 72 MB is used, but only 891 GB is available for use. What is causing the nearly 47 GB overhead?
There should be a 5% difference due to space reserved for use by the root user (and this seems your case, as the difference is exactly 5% of the total space).
However, I have also found reference on some Oracle documents about df reporting only 90% of maximum available space, the remaining 10% being left as "buffer" for better performances.
Displaying Disk Space Statistics (df)
Use the df command to show the amount of free disk space on each mounted disk. The usable disk space that is reported by df reflects only 90 percent of full capacity, as the reporting statistics leave a 10 percent above the total available space. This head room normally stays empty for better performance.
