Side-by-side specifications of the Synology FS3600 and FS6400, from official datasheets. Differences are highlighted.
| FS3600 | FS6400 | |
| CPU | Intel Xeon D-1567 | 2 × Intel Xeon Silver 4110, 2.1/3.0 GHz |
| Cores / threads | 12 cores / 24 threads | 16 cores / 32 threads total |
| RAM (base) | 16 GB DDR4 ECC RDIMM | 32 GB DDR4 ECC RDIMM |
| RAM (max) | 128 GB | 512 GB |
| Drive bays | 24 | 24 × 2.5-inch SAS HDD/SSD or SATA SSD |
| Expandable to | 72 | 48 with 2 × RX1222sas; 72 with 2 × FX2421 |
| M.2 slots | 0 | 0 |
| Network | 4×1GbE RJ-45, 2×10GbE RJ-45 | 2 × 1GbE RJ-45; 2 × 10GbE RJ-45 |
| 10GbE | yes | yes |
| Max raw capacity | 92.16 TB | 184.32 TB raw internal |
| Hot-swap | yes | yes |
| Form factor | 2U rackmount | 2U rackmount |
| Released | 2017 | 2018 |
| Power consumption | 258.23 W / 127.99 W | 288.49 W / 145.8 W |
| DSM at launch | 6.1 | — |
Choose the FS6400 if you need a much larger all-flash system: it uses dual Intel Xeon D-1541 CPUs, supports up to 512 GB RAM, has 24 bays with expansion support, and includes built-in 10GbE plus M.2 slots. The FS3600 is the smaller/cheaper option with a single Intel Xeon D-1567, up to 128 GB RAM, 24 bays but no expansion, and it also has built-in 10GbE and M.2. For most home/SMB buyers, the FS3600 is enough unless you need the FS6400’s extra CPU and memory headroom for heavier virtualization or more users.