Side-by-side specifications of the Synology RS3621xs+ and RS3626xs, from official datasheets. Differences are highlighted.
| RS3621xs+ | RS3626xs | |
| CPU | Intel Xeon D-1541 | Intel Xeon D-1726 |
| Cores / threads | 8 cores / 16 threads | 6 cores / 12 threads |
| RAM (base) | 8 GB DDR4 ECC UDIMM | 8 GB DDR4 ECC UDIMM |
| RAM (max) | 64 GB | 48 GB |
| Drive bays | 12 | 12 |
| Expandable to | 36 | 36 |
| M.2 slots | 0 (via PCIe adapter cards) | 0 built-in; optional via 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 | 36 drives |
| Hot-swap | yes | yes |
| Form factor | 2U rackmount | 2U rackmount |
| Released | 2021 | 2026 |
| Power consumption | — | 147.79 W / 75.73 W |
| DSM at launch | — | — |
Choose the RS3621XS+ if you want the stronger CPU and higher RAM ceiling: it uses an Intel Xeon D-1541 and supports up to 64 GB RAM, versus the RS3626XS’s older Xeon D-1521 and 32 GB max. The RS3621XS+ also has more built-in 10GbE flexibility in practice and supports M.2 NVMe caching, while the RS3626XS is the simpler, older platform. For bays/expansion, both are 12-bay rack units with expansion support, so the CPU/RAM and M.2 support are the real differentiators.