Side-by-side specifications of the Synology RS4021xs+ and RS4826xs+, from official datasheets. Differences are highlighted.
| RS4021xs+ | RS4826xs+ | |
| 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 | 12 |
| Expandable to | 40 (with 2× RX1217/RX1217RP) | 48 |
| M.2 slots | Optional via PCIe adapter cards | 0 |
| 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 | 48 drives |
| Hot-swap | yes | yes |
| Form factor | 3U rackmount | 2U rackmount |
| Released | 2021 | 2026 |
| Power consumption | 145.79 W / 62.68 W | 155.24 W / 76.15 W |
| DSM at launch | — | — |
Choose the RS4826xs+ if you want the newer platform: it uses a much stronger CPU, supports a higher RAM ceiling, has more bays, and includes 10GbE and M.2 built in. The RS4021xs+ is the older, simpler choice only if you’re fine with fewer bays, lower expandability, and don’t need the extra onboard networking/cache features.