I started with a Seagate Barracuda 1TB HDD. Then I added a couple WD Black 1TB HDDs one at a time. Realizing I was running out of room, I bought a WD Black 6TB HDD. At one point I bought a Plextor 250 GB M5 Pro SSD for the OS, programs, and a game or two that requires a faster drive. When games started getting gargantuan file size, I realized "I'm gonna need a bigger drive" (cue the Jaws flashback). Just when NVMe drives seemed to start getting sane in prices, I bought a Samsung 970 EVO 500 GB for $116. Now all I look for is good deals on 2TB NVMe drives. Lately I'm looking at the Corsair MP600 2TB.
I still have a lot of games on my 1TB HDDs, I use the 6TB one mostly to store uninstalled games and for video capture. I also still sometimes install new games on one of the WD Black 1TB drives after clearing some space, like the remastered Mass Effect Legendary trilogy, which is near 80 GB. I'm REALLY getting tired of having to clear space on my 970 EVO when I need to install a new game, and often times lately, the ones I uninstall I haven't even finished yet. Then again, there ae a lot of games these days that aren't nearly as good as I thought they'd be. You have to learn to quell that itch to play new games in times like these unless you have endless storage.
I have to say though, that 6TB HDD is way faster than I thought it would be. NVMe drives are insanely fast, but what I hate about them is they suck up too many SATA ports at full speed. I will have to pull out my Seagate Barracuda 1TB HDD or the Plextor 250 GB M5 Pro just to have a SATA port open for the 2TB NVMe drive, and even then, I'll have to run it at x2 speed instead of x4, so I won't get the full speed. This is the way I set up my 970 EVO, the read speed doesn't suffer much, but it took the write speed down to about 2500 Mb/s, still way more speed than games need though. Who would of thought storage drives would become one of the most talked about components!
All these drives fit inside my case btw. I have a rather large one, it's an Antec DF-85. It also came with built-in hardware to do drive hotswaps in 4 bays, but I haven't needed to use them yet. The next MB I get will have more SATA ports, I hope.