Side-by-side specifications of the Synology RS409 and RS409RP+, from official datasheets. Differences are highlighted.
| RS409 | RS409RP+ | |
| CPU | 1.2GHz | unknown |
| Cores / threads | — | unknown |
| RAM (base) | 256MB | unknown |
| RAM (max) | — | unknown |
| Drive bays | 4 | 4 |
| Expandable to | 4 | 4 (via RX4) |
| M.2 slots | 0 | 0 |
| Network | 2x Gigabit | 2 x Gigabit |
| 10GbE | no | no |
| Max raw capacity | 3TB | 8 drives |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | — | 2009 |
| Power consumption | 52.8 W / 23 W | 61 W / 29 W |
| DSM at launch | 2.1 | 2.1 |
Choose the RS409RP+ if you need more headroom: it has the faster “+” CPU, more RAM capacity, and redundant power supplies, while both are 4-bay units with no built-in 10GbE or M.2. Neither model has 10GbE or M.2, and neither is a bay-count or expansion upgrade over the other.