Side-by-side specifications of the Synology DS1520+ and DS1621xs+, from official datasheets. Differences are highlighted.
| DS1520+ | DS1621xs+ | |
| CPU | Intel Celeron J4125 | Intel Xeon D-1527 |
| Cores / threads | 4-core | 4 cores |
| RAM (base) | 8 GB | 8 GB |
| RAM (max) | 8 GB | 32 GB |
| Drive bays | 5 | 6 |
| Expandable to | 15 | 16 |
| M.2 slots | 2 | 2 |
| Network | 4 x 1GbE RJ-45 | 2x1GbE, 1x10GbE |
| 10GbE | no | yes |
| Max raw capacity | 80 TB | 256 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2022 | 2020 |