To diagnose and improve slow Synology file transfers, the knowledge base suggests these checks:
1. Test whether the network path is the problem
- Connect your client PC and NAS directly with an Ethernet cable.
- If transfer speed increases, the router, switch, or other network device may be the issue, or its configuration may need checking. [7]
2. Check network status in DSM
- Go to Control Panel > Network > Network Interface.
- Verify the Network Status shows the correct link speed for the port in use:
- RJ-45 1GbE LAN Port: 1000 Mbps
- RJ-45 10GbE LAN Port: 10000 Mbps
- SFP+ 10GbE LAN Port: 10000 Mbps [7]
3. Check MTU consistency
- Make sure the MTU in Network Status matches the MTU of the client PC and all other network devices. [7]
4. For Windows SMB slowness, try these checks
- Make sure the client device is not busy or running any .exe files during transfer.
- Try different file protocols to see whether the problem is specific to Windows file services.
- Enable DHCP, then connect the Synology system and client directly with a cable without a router or switch in between, and in Control Panel > Network > Network Interface > Edit, tick Get network configuration automatically (DHCP).
- Make sure MTU settings are identical with your Synology product.
- Disable all firewall or antivirus software. [8]
5. Improve general network performance
- Synology recommends Link Aggregation when multiple LAN ports are available. It combines multiple LAN interfaces to increase bandwidth and throughput and provides traffic failover. [1]
6. Consider SSD cache for frequently accessed data
- Synology recommends using SSD Cache Advisor in Storage Manager to calculate a proper cache size based on recently accessed files. [1]
If you’re using a Synology Router and the problem is Wi‑Fi or internet speed, the knowledge base also points to checks like Traffic Control/Monitor, TTL settings, cable changes, and testing another LAN port/device. [10][11]
Sources used: [1], [7], [8], [10], [11]