A couple considerations:

- 8 drives is the number where Synology firmly separates "hobbyist" from "SOHO." 12 drives is where they separate "SOHO" from "Enterprise."

- The numbers you care about are DS2-, DS4-, DS6-, DS7-, DS9-, DS15-, DS16-, and DS18-. That stands for "Disk Station" where 2, 4, 6 are basic-bitch with that many drives, 7 and 9 are value-add with expansion and 15, 16 and 18 are their SOHO sizes that expand a lot. The numbers after the dash (which is a convention I have added for simplicity) is generation number. Thus a DS214 is a 4th generation 2-drive model. A DS214 plus is a 4th generation 2-drive model with slight revision, like maybe a little more memory. Thus, the 1813 plus I was running is eight generations older than the 1821 plus they're currently selling, but they're both 8-drive, fully-expandable models. Things only get tricky when you buy expansion chassis, because some expansion chassis bridge generations but it's not obvious.

- Synology, if they aren't dead, go for a lot used. It's like they're Macs or something. A 1621 is a thousand dollars off Amazon. A 1618, which is three generations old, is $700 rode hard put away wet on eBay with no pedigree. I sold my busted one for $250 (I think?). I sold the expansion, which I bought used, for more than I bought it used for, having used it for four years. DS214s go for around $150 used; I bought ours new for $179? $229? seven goddamn years ago.