Side-by-side specifications of the Synology RS2421+ and RS2421RP+, from official datasheets. Differences are highlighted.
| RS2421+ | RS2421RP+ | |
| CPU | AMD Ryzen V1500B | AMD Ryzen V1500B |
| Cores / threads | 4 cores / 8 threads | 4 cores / 8 threads |
| RAM (base) | 4 GB DDR4 ECC UDIMM | 4 GB DDR4 ECC UDIMM |
| RAM (max) | 32 GB | 32 GB |
| Drive bays | 12 | 12 |
| Expandable to | 24 total with 1 RX1217/RX1217RP | 24 total with 1x RX1217/RX1217RP |
| M.2 slots | 0 internal; via PCIe adapter | 0 internal; optional PCIe adapter |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 108 TB single volume; 24 bays with expansion | 108 TB per volume; 24 bays with expansion |
| Hot-swap | yes | yes |
| Form factor | Rackmount 2U | Rackmount 2U |
| Released | 2021 | 2021 |
| Power consumption | — | — |
| DSM at launch | — | — |
They’re effectively the same unit: both use the same Ryzen V1500B CPU, max out at 32 GB RAM, have 12 bays with support for the same expansion shelves, and neither includes built-in 10GbE or M.2 SSD slots. The only real differentiator is the RP in RS2421RP+, which adds dual redundant power supplies for higher uptime. For a home/SMB buyer, pick the cheaper RS2421+ unless you specifically want redundant power.