Side-by-side specifications of the Synology DS1621xs+ and DS1815+, from official datasheets. Differences are highlighted.
| DS1621xs+ | DS1815+ | |
| CPU | Intel Xeon D-1527 2.2/2.7 GHz | Intel Atom C2538 |
| Cores / threads | 4 cores / 8 threads | 4 cores / 4 threads |
| RAM (base) | 8 GB DDR4 ECC SODIMM | 2 GB DDR3 |
| RAM (max) | 32 GB | 6 GB |
| Drive bays | 6 | 8 |
| Expandable to | 16 total with 2× DX517 | 10 (DX513; 18 total) |
| M.2 slots | 2× M.2 2280 NVMe | 0 |
| Network | 2× 1GbE RJ-45, 1× 10GbE RJ-45 | 4x Gigabit Ethernet |
| 10GbE | yes | no |
| Max raw capacity | 96 TB internal; 256 TB with 2× DX517 | 48 TB internal; 108 TB with DX513 expansion |
| Hot-swap | yes | yes |
| Form factor | Tower | Tower |
| Released | 2020 | 2014 |
| Power consumption | — | — |
| DSM at launch | — | — |