Side-by-side specifications of the Synology RS815 and RS815+, from official datasheets. Differences are highlighted.
| RS815 | RS815+ | |
| CPU | dual-core CPU | Intel Atom C2538 2.4GHz |
| Cores / threads | 2 cores / 2 threads | 4 cores / 4 threads |
| RAM (base) | 1 GB DDR3 | 2 GB DDR3 |
| RAM (max) | 1 GB | 6 GB |
| Drive bays | 4 | 4 |
| Expandable to | 4 | 4 (up to 8 with RX415) |
| M.2 slots | 0 | 0 |
| Network | 2x Gigabit | 4x Gigabit |
| 10GbE | no | no |
| Max raw capacity | 32 TB | 24 TB internal; 48 TB with RX415 |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | 2015 | 2015 |
| Power consumption | — | — |
| DSM at launch | — | — |
Choose the RS815+ if you need more headroom: it has a faster CPU, more RAM capacity, and better overall performance for heavier SMB use. Both are 4-bay units with no native 10GbE or M.2 support, and neither is meant for expansion to a larger bay count; the RS815 is the cheaper, more basic pick if you only need simple file storage.