Side-by-side specifications of the Synology DS1522+ and DS1621+, from official datasheets. Differences are highlighted.
| DS1522+ | DS1621+ | |
| CPU | AMD Ryzen R1600 2.6 GHz, up to 3.1 GHz | AMD Ryzen V1500B, 2.2 GHz |
| Cores / threads | 2 cores / 4 threads | 4 cores / 8 threads |
| RAM (base) | 8 GB DDR4 ECC SODIMM | 4 GB DDR4 ECC SODIMM |
| RAM (max) | 32 GB | 32 GB (16 GB x 2) |
| Drive bays | 5 | 6 |
| Expandable to | 10 | 16 total with 2 DX517 units |
| M.2 slots | 2 M.2 2280 NVMe | 2 x M.2 2280 NVMe |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 15 drives | 256 TB raw with 2 DX517 units |
| Hot-swap | yes | yes |
| Form factor | Desktop | desktop |
| Released | 2021 | 2020 |
| Power consumption | 52.06 W / 16.71 W | 51.22 W / 25.27 W |
| DSM at launch | — | — |
Choose the DS1621+ if you want the stronger platform: it has the better CPU, supports up to 32 GB RAM, has 6 bays instead of 5, and expands farther; it also offers 10GbE expansion but no built-in 10GbE, and it uses M.2 slots for SSD cache. Choose the DS1522+ if you want the newer, simpler 5-bay unit with built-in 2.5GbE and M.2 cache slots, but it has a weaker CPU and a lower RAM ceiling than the DS1621+.