Ubuntu – Understanding Why I have lost so much space mounting a new HDD

hard drivemount

I've just purchased a 4TB Western Digital Red hard disk for my Media Server. I want to understand why I've ended up losing so much space by formatting it as ext4 and then mounting it. I understand some will be lost for the drives own files but what I have lost seems a bit much.

Steps I have taken:

Formatted the Drive using sudo mkfs.ext4 /dev/sde

Edited FS tab so it auto mounts at boot 

UUID=3276bc13-20a5-4225-ad33-d8fecdd5216c /wd_red_1 ext4 defaults 0 0

Now when I run df -h this is my output

/dev/sde        3.6T   89M  3.4T   1% /wd_red_1

Does it not seem a bit much that in total I have lost 700GB of space?

In comparison I've got a seagate 2TB HDD which I've been through the same process with and it's only taken 200GB (so I have 1.8TB usable). Have I done something wrong?

Server is running 18.04.3 LTS

Best Answer

Disc manufacturers list the size in decimal values, so your 4TB HD is actually 4,000,000,000,000 Bytes. But df -h lists in binary base numbers (i.e. 4KB is 4096 Bytes, 4MB is 4,194,304 Bytes, 4GB is 4,294,967,296 Bytes, and 4TB is 4,398,046,511,104 Bytes. You only bought a disc with 4,000,000,000,000 Bytes, so that works out to 3.63798807 TB (in the binary number base). This is pretty much exactly the value that you're seeing listed by df -h.

You didn't lose any capacity, it's just a numbers game played by the manufacturers.

To check this, try df -H. With a capital H, it lists it in decimal values, so instead of "3.6T" it will say "4T" or very close to that number. The manufacturers even go further and the "4TB" they list is also approximate. The actual may be slightly more or less than that.

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