Side-by-side specifications of the Synology DS1517 and DS1621+, from official datasheets. Differences are highlighted.
| DS1517 | DS1621+ | |
| CPU | Annapurna Labs AL-314 | AMD Ryzen V1500B |
| Cores / threads | 4 | 4 |
| RAM (base) | 2 GB | 4 GB |
| RAM (max) | 16 GB | 32 GB |
| Drive bays | 5 | 6 |
| Expandable to | 15 | 16 |
| M.2 slots | 2 | 2 |
| Network | 4x1GbE | 4x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 75 TB | 256 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2016 | 2020 |