nice size, its a shame this will only format to about 2.7TB so you lose about 300GB!
You don't 'lose' anything. It was never there (well, OK, some of it was if you count ECC data and the like).
3.0TB ~ 3,000,000,000,000 bytes ~ 2.728 TiB
It's all down to what units you use. Hard disk manufacturers use SI (mega, giga, tera), computers use IEC (mebi, gibi, tebi). Unfortunately, most computers still display GB where they mean GiB, etc.
I calculate if I slapped in 4 of these it'll give me 8.5TB of storage from 12TB of total.
I make it 8.1 TiB.