This thread has quite a lot of info on this matter, you might want to check it out:
I believe more and more manufacturers now give this info: When buying a disk, it’s usually indicated these days. But back then, yeah… that was quite difficult to know whether a disk was SMR or CMR.
I’m no disk expert but from my experience, if you stick with recommandations like having one node per disk, any CMR disk will do really. Even 2.5" disks (as long as they are CMR) can cope with Storj activity without problem (even during extensive tests Storj was carrying out at some point in the past: 200GB/day for a short period: my 2.5" CMR was just fine, and all my SMR disks stalled and failed miserably 
).
Just be sure to have enough power when plugging a disk to a RPi as these minicomputers are known to provide weak power to USB devices:
- If you’re using 3.5" disks, then they will come with their own power supply so it should be fine.
- If you’re using 2.5" disks, then you need to make they have their own power supply, or that you use a powered USB HUB that can provide enough power for all the disks you wanna plug to it.
Also, you want the USB HUB to have physical switches, so it stays ON in case of power outage. For example, I use this one for powering 3x 2.5" disks and the RPi 4B itself:
https://www.amazon.co.uk/gp/product/B07N5FTPRM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
(This is for information only, I’m not saying you should buy this, and this link is not an affiliate link)