Side-by-side specifications of the Synology RS4021xs+ and RS6426xs+, from official datasheets. Differences are highlighted.
| RS4021xs+ | RS6426xs+ | |
| CPU | Intel Xeon D-1541 | Intel Xeon D-1739 |
| Cores / threads | 8 cores / 16 threads | 8 cores / 16 threads |
| RAM (base) | 16 GB DDR4 ECC UDIMM | 16 GB DDR4 ECC RDIMM |
| RAM (max) | 64 GB | 96 GB |
| Drive bays | 16 | 16 |
| Expandable to | 40 (with 2× RX1217/RX1217RP) | 64 |
| M.2 slots | Optional via PCIe adapter cards | 0 (via optional adapter card) |
| Network | 4× 1GbE RJ-45; 2× 10GbE RJ-45 | 2 × 10GbE RJ-45 + 1 × out-of-band management LAN |
| 10GbE | yes | yes |
| Max raw capacity | 1 PB single volume | 64 drives |
| Hot-swap | yes | yes |
| Form factor | 3U rackmount | 3U rackmount |
| Released | 2021 | 2026 |
| Power consumption | 145.79 W / 62.68 W | 165.45 W / 73.38 W |
| DSM at launch | — | — |