The mid size versions have 3 drive bays (2x 3.5", one 2.5") plus an optical bay, but only 3 SATA connectors (which was really odd to me). You can find dual SATA adaptors for the “WiFi” M.2 slot if you want to use an adaptor for a 2.5" drive on the optical bay. But if you want more than 4 drives, you’ll need to get creative mounting them.
The mid size versions have 3 drive bays (2x 3.5", one 2.5") plus an optical bay, but only 3 SATA connectors (which was really odd to me). You can find dual SATA adaptors for the “WiFi” M.2 slot if you want to use an adaptor for a 2.5" drive on the optical bay. But if you want more than 4 drives, you’ll need to get creative mounting them.