Not THAT unusual, but... I have a Dell R520 server that was leftover/retired from work. I mostly use it for storage due to the amount of disk trays it has. I have all of these disks in a ZFS pool, leaving no actual drives for the OS. However, this was an old VM server, so it has an internal USB 2 port and a ridiculous amount of RAM, so the OS is booted from USB, and I don't use swap.

Boot performance is abysmal (on the rare occasion where I actually need to reboot), but once booted I notice no real downside to having the OS itself on really slow storage. Sure, it's somewhat slow to do os-related stuff such as apt-get, but it's not like I'm in a hurry when doing it. Plus other than updating stuff, the OS storage doesn't see a whole lot of changes/writes.

Now I just need to figure out how to economically attach these 40 additional SAS drives I have. It doesn't have to look good (i.e. fit in the same chassis. Or any chassis at all, for that matter), it just have to work. These additional drives are only 4TB each, but they were free.