Side-by-side specifications of the Synology RS815+ and RS815RP+, from official datasheets. Differences are highlighted.
| RS815+ | RS815RP+ | |
| CPU | Intel Atom C2538 2.4GHz | Intel Atom C2538 2.4GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 4 threads |
| RAM (base) | 2 GB DDR3 | 2 GB DDR3 |
| RAM (max) | 6 GB | 6 GB |
| Drive bays | 4 | 4 |
| Expandable to | 4 (up to 8 with RX415) | 4 (with RX415) |
| M.2 slots | 0 | 0 |
| Network | 4x Gigabit | 4x Gigabit |
| 10GbE | no | no |
| Max raw capacity | 24 TB internal; 48 TB with RX415 | 24 TB internal; 48 TB with expansion |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | 2015 | 2015 |
| Power consumption | — | — |
| DSM at launch | — | — |
Pick the RS815RP+ only if you need the redundant power supplies; otherwise the RS815+ is the same class of 4-bay NAS and is usually the better-value buy. The decisive hardware differences are effectively minimal here: same CPU tier, same RAM ceiling, same 4 bays and no expansion, and neither model offers built-in 10GbE or M.2.