Side-by-side specifications of the Synology DS1817 and DS1821+, from official datasheets. Differences are highlighted.
| DS1817 | DS1821+ | |
| CPU | Intel Atom C2538 1.7 GHz | AMD Ryzen V1500B 2.2 GHz |
| Cores / threads | quad-core/4 threads | 4 cores / 8 threads |
| RAM (base) | 4 GB | 4 GB DDR4 ECC SODIMM |
| RAM (max) | 8 GB | 32 GB |
| Drive bays | 8 | 8 |
| Expandable to | 10 | 10 (up to 18 with 2 DX517) |
| M.2 slots | 0 | 2 x M.2 2280 NVMe |
| Network | 2 x 1GbE RJ-45, 2 x 10GBASE-T RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | yes | optional |
| Max raw capacity | 180 TB | 288 TB raw with 2 DX517 |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2017 | 2020 |
| Power consumption | — | 59.8 W / 26.18 W |
| DSM at launch | — | — |