Side-by-side specifications of the Synology RS3617xs and RS3618xs, from official datasheets. Differences are highlighted.
| RS3617xs | RS3618xs | |
| CPU | Intel Xeon E3-1230v2 3.3GHz | Intel Xeon D-1521 |
| Cores / threads | 4 cores / 8 threads | 4 cores / 8 threads |
| RAM (base) | 4GB DDR3-1600 ECC | 8 GB DDR4 ECC UDIMM |
| RAM (max) | 32GB | 64 GB |
| Drive bays | 12 | 12 |
| Expandable to | 24 | 36 total with 2 expansion units |
| M.2 slots | 0 | 0 |
| Network | 4x 1GbE RJ-45 | 4 × 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 96TB internal; 288TB with 2 expansion units | 216 TB |
| Hot-swap | yes | yes |
| Form factor | 2U rackmount | 2U rackmount |
| Released | 2017 | 2018 |
| Power consumption | — | 142.76 W / 55.05 W |
| DSM at launch | — | — |
Pick the RS3618xs if you want the newer platform: it uses a faster CPU, supports more RAM, and includes better native 10GbE options; the RS3617xs is older and generally weaker on performance and memory ceiling. Bay count and expansion are effectively the same class, and neither model has built-in M.2 NVMe slots.