It's possible but you're limiting yourself to 2 or 4 UDB drive mirrors. If you just want a zfs storage pool and aren't too picky about anything else, it works, but if your list of expectations goes beyond a place to dump data, you're setting yourself up to be frustrated later.
My home net has several pi3 and pi4 systems that boot off a small SD card and then mounts working storage via iSCSI, which works great for how I use them. There's no reason I couldn't serve that off a pi, but their limited IO and memory makes them a poor choice.
My home net has several pi3 and pi4 systems that boot off a small SD card and then mounts working storage via iSCSI, which works great for how I use them. There's no reason I couldn't serve that off a pi, but their limited IO and memory makes them a poor choice.