Credit for the original models:
https://www.printables.com/model/40826-35-generic-hdd-caddy
https://www.printables.com/en/model/383555-hdd-expandable-rack-v1

I made a NAS in an old PC case. Couldn't find the original HDD rack, I removed it years ago and probably threw it away or something, so I had to print one.
After some looking I found these files which did what I needed, and edited them a bit. Decided to share them here.

Since I needed to print 6 of these, I wanted to reduce print time and material usage as much as possible.
I removed a lot of unnecessary geometry from the caddy, which for me resulted in a significant reduction in material (about a 30% reduction) and 1 less hour of print time for each print which saved me 6 hours in total. The caddy needs supports for buildplate only for the slides to print correctly. You can print them as overhangs too but they might come out a bit ugly. It's really just a few mm of Z height so I suggest using supports.

For the stackable rack, everything was mostly OK. I removed the pins on the sides for the original stack locking system as I found using them would make the thing more wobbly than I would have wanted and needed supports to print correctly. Instead I opted to just glue each rack module together with the next. other than that I added a few chamfers, all together they make the model printable with no supports.

I'm also including my mounting system. Consider it mostly just an example since it's very specifically made to be use on my PC case. You'll most likely just have to come up with your solution. Mine was made to offset the whole assembly up of 15mm to clear the edge of the case, and it's mounted to some pre-existing holes in the bottom of the case through m3 screws and heat-set inserts.