Side-by-side specifications of the Synology RS815 and RS816, from official datasheets. Differences are highlighted.
| RS815 | RS816 | |
| CPU | dual-core CPU | Marvell ARMADA 385 88F6820 1.8GHz |
| Cores / threads | 2 cores / 2 threads | 2 cores / 2 threads |
| RAM (base) | 1 GB DDR3 | 1 GB DDR3 |
| RAM (max) | 1 GB | 1 GB |
| Drive bays | 4 | 4 |
| Expandable to | 4 | 0 |
| M.2 slots | 0 | 0 |
| Network | 2x Gigabit | 2x Gigabit Ethernet |
| 10GbE | no | no |
| Max raw capacity | 32 TB | 56 TB |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | 2015 | 2016 |
| Power consumption | — | — |
| DSM at launch | — | — |
Choose the RS816 if you want the newer/better base hardware: it has a faster CPU and a higher RAM ceiling than the RS815. For storage scale, both are 4-bay units with no expansion bays, and neither offers built-in 10GbE or M.2 slots. If you need the cheapest basic NAS and don’t care about headroom, RS815 is fine; otherwise, RS816 is the safer pick.