Side-by-side specifications of the Synology DS1621xs+ and DS1821+, from official datasheets. Differences are highlighted.
| DS1621xs+ | DS1821+ | |
| CPU | Intel Xeon D-1527 2.2/2.7 GHz | AMD Ryzen V1500B 2.2 GHz |
| Cores / threads | 4 cores / 8 threads | 4 cores / 8 threads |
| RAM (base) | 8 GB DDR4 ECC SODIMM | 4 GB DDR4 ECC SODIMM |
| RAM (max) | 32 GB | 32 GB |
| Drive bays | 6 | 8 |
| Expandable to | 16 total with 2× DX517 | 10 (up to 18 with 2 DX517) |
| M.2 slots | 2× M.2 2280 NVMe | 2 x M.2 2280 NVMe |
| Network | 2× 1GbE RJ-45, 1× 10GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | yes | optional |
| Max raw capacity | 96 TB internal; 256 TB with 2× DX517 | 288 TB raw with 2 DX517 |
| Hot-swap | yes | yes |
| Form factor | Tower | desktop |
| Released | 2020 | 2020 |
| Power consumption | — | 59.8 W / 26.18 W |
| DSM at launch | — | — |