The largest disk is 8TB which was installed as D: hosts iTunes and the Steam Library along with Origin and Uplay. Larger disks ranging to 16 TB. HAMR disks are likely to be available in later 2020 which will bump up capacity from 20TB and beyond to eventually near 60TB or more.
With the 8TB disk and a pair of 4TB disks the machine has 16GB of total storage with 2 free drive bays. At present there is adequate storage to handle the entire game library. Additional storage would allow some options should a disk fault emerge.
Steam games currently are 3.72 TB which requires a fair bit of time to copy from one hard disk to another. This is why the 8 TB disk was procured. The hope is that this disk can contain the game collection for at least a few months.
To speed up the copying of files, disabling the real time security scan will make the process a lot laster. The security will be enabled when a machine is rebooted.
Steam games are often made up of a lot of small files which can slow the copy process considerably. There is not much that can be done as a lot of independent game developers do not use the packed archives that larger studios use.
Speeds reached over 200 MB/s with large media files. Games tended to be slower and often fall below 1 MB/s when small files are abundant.
The advantage of the large disk is obvious. There is so much room its unlikely to be overwhelmed anytime soon.
Eventually the 512 GB SSD will be replaced and a larger capacity model. The main reason is that actively played games can be moved to the SSD while the remaining collection can reside on a hard disk. The new Intel 666p should surface eventually at NewEgg.
The HAF 932 has 5 disk bays so it can be provisioned with a lot of storage. The MSI X470 has dual M.2 slots which would permit the option of more SSD storage. Choices galore for gaming.