Side-by-side specifications of the Synology DS1517 and DS1621xs+, from official datasheets. Differences are highlighted.
| DS1517 | DS1621xs+ | |
| CPU | Annapurna Labs Alpine AL-314 1.7GHz | Intel Xeon D-1527 2.2/2.7 GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 8 threads |
| RAM (base) | 2 GB DDR3L | 8 GB DDR4 ECC SODIMM |
| RAM (max) | 2 GB | 32 GB |
| Drive bays | 5 | 6 |
| Expandable to | 10 (2× DX517) | 16 total with 2× DX517 |
| M.2 slots | 0 | 2× M.2 2280 NVMe |
| Network | 4× 1GbE RJ-45 | 2× 1GbE RJ-45, 1× 10GbE RJ-45 |
| 10GbE | no | yes |
| Max raw capacity | 75 TB | 96 TB internal; 256 TB with 2× DX517 |
| Hot-swap | yes | yes |
| Form factor | Desktop | Tower |
| Released | 2017 | 2020 |
| Power consumption | 39.5 W / null | — |
| DSM at launch | — | — |