20TB installed, but only 17TB usable?

Purchased a new Drobo 5D with 5 WD 4TB HDs, after formatting I expect to lose a couple of megs, or even gigs, but to lose 2TB? I’m thinking that this is a bit odd… It’s formatted as Mac OS Extended (Journaled), it’s primarily used as storage for my iTunes Media.

Any reason why I would lose 2TB of storage right after install and formatting?

Any help would be appreciated.


Hi there.

That’s because of different definitions. Basically 1 MB is defined as one million bytes, 1 GB is defined as one billion bytes, and so on, but since your computer uses a binary system, you may notice a discrepancy between your hard drive’s published capacity and the capacity acknowledged by your computer.

For example, a hard drive that is said to contain 10 GB of storage space using a decimal system is actually capable of storing 10,000,000,000 bytes. However, in a binary system, 10 GB is 10,737,418,240 bytes and as a result, instead of acknowledging 10 GB, your computer will acknowledge 9.31 GB. This is not a malfunction, but a matter of different definitions.

Hope this helps.

Cheers! :slight_smile:

Welcome to the world of hard drive marketing!

its also like a big box of cornflakes… when you open it up, you can fit half your arm inside before you can reach the flakes :slight_smile: