Harmy said:

So, I've hit a bit of a snag with the new computer - on each of the discs, there's exactly 746.52GB on each of the 3TB drives that the system simply refuses to allocate to a partition. I tried looking for solutions online but no luck - so far, I only managed to find out that I'm far from being the only one with this problem.

You partitioned the HDDs with MBR rather than GPT. MBR only partitions up to ~2.19GiB, hence your loss of 746.52GiB.

Here's a detailed explanation of your problem (see post 2): http://forums.seagate.com/t5/Desktop-HDD-Desktop-SSHD/Hooking-up-3TB-seagate-barracuda-drive/td-p/102204

GPT FAQ from M$: http://msdn.microsoft.com/en-us/library/windows/hardware/gg463525.aspx

Are these internal or external HDDs? If external, then what enclosure are you using and how are you connecting it to the computer (e.g., eSATA, USB)?