Side-by-side specifications of the Synology RS2418RP+ and RS2421RP+, from official datasheets. Differences are highlighted.
| RS2418RP+ | RS2421RP+ | |
| CPU | Intel Atom C3538 | AMD Ryzen V1500B |
| 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 | 12 | 12 |
| Expandable to | 12 | 24 total with 1x RX1217/RX1217RP |
| M.2 slots | 0 (via optional adapter card) | 0 internal; optional PCIe adapter |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 288 TB | 108 TB per volume; 24 bays with expansion |
| Hot-swap | yes | yes |
| Form factor | 2U rackmount | Rackmount 2U |
| Released | 2018 | 2021 |
| Power consumption | 119.6 W / 55.9 W | — |
| DSM at launch | 6.2 | — |
Choose the RS2421RP+ for its newer AMD Ryzen V1500B CPU, 32GB maximum RAM, and two built-in M.2 NVMe slots for SSD caching. Both provide 12 bays with expansion support, but neither includes 10GbE; the RS2418RP+ uses an older Intel Atom C2538 CPU, supports 32GB RAM, and lacks M.2 slots.