Side-by-side specifications of the Synology RS2818RP+ and RS2821RP+, from official datasheets. Differences are highlighted.
| RS2818RP+ | RS2821RP+ | |
| CPU | Intel Atom C3538 | AMD Ryzen V1500B, 2.2 GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 8 threads |
| RAM (base) | 4 GB DDR4 non-ECC UDIMM | 4 GB DDR4 ECC UDIMM |
| RAM (max) | 64 GB | 32 GB |
| Drive bays | 16 | 16 |
| Expandable to | 12 | 28 |
| M.2 slots | 0 (via optional adapter card) | 0 internal; optional via PCIe adapter |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 336 TB | 108 TB single volume |
| Hot-swap | yes | yes |
| Form factor | 3U | Rackmount 3U |
| Released | 2018 | 2021 |
| Power consumption | 138.1 W / 66.7 W | 97.54 W / 49.57 W |
| DSM at launch | — | — |
Choose the RS2821RP+ if you want the newer, much faster AMD V1500B CPU and a higher RAM ceiling: 32GB vs 64GB. Both are 8-bay units with the same expansion path via RX418, and both can do 10GbE only by adding an optional PCIe card; neither has built-in 10GbE or M.2 slots. If you’re cost-sensitive and only need basic NAS duties, the RS2818RP+ is the cheaper older platform.