Experiencing very slow transfer speeds on your Asustor NAS—often stuck around 8 Mbps—can be frustrating, especially with large files. Slow throughput typically traces back to network configuration, hardware bottlenecks, or software settings. Use the guide below to diagnose and fix the most common causes.
Common Causes and How to Fix Them
1. Network Link Speed and Cabling
Your NAS and PC should both negotiate a 1 Gbps (or faster) Ethernet link. Anything less (e.g., 100 Mbps) will cap performance and can show up as single-digit MB/s speeds in copy dialogs.
Solution:
- Verify link speed on both ends. In ADM, check Settings > Network; on your PC, check the network adapter’s Status to confirm it’s at 1.0 Gbps/Full Duplex.
- Use quality Cat 5e or Cat 6 cables and a Gigabit-capable switch/router. Avoid damaged cables, powerline adapters, and Wi‑Fi for large file transfers.
- If possible, test with a direct connection (PC ↔ NAS) using a known-good cable and static IPs to rule out switch/router issues.
- Learn more about Gigabit Ethernet capabilities: Gigabit Ethernet overview.
2. Jumbo Frames and MTU Mismatch
Jumbo Frames can improve performance in some environments, but inconsistent MTU settings between devices often cause fragmentation and severe slowdowns.
Solution:
- Keep MTU at the default 1500 unless you control every device in the path (NAS, PC, switch) and can set them identically.
- If you previously enabled Jumbo Frames, disable them or ensure the same MTU is configured everywhere.
- Background on Jumbo Frames: Intel’s guidance on Jumbo Frames.
3. Switch/Router Limitations and Duplex Issues
Older or mixed-speed network gear can force 10/100 links or create duplex mismatches, both of which reduce throughput.
Solution:
- Confirm all ports involved are Gigabit-capable and not limited to 10/100.
- Re-seat cables and reboot switches/routers to reset auto‑negotiation. If problems persist, try a different switch port or a different switch.
4. Disk Performance and NAS Workload
Old, failing, or heavily loaded drives (e.g., during RAID rebuilds) can bottleneck transfers.
Solution:
- Open Asustor Storage Manager to check SMART status, bad sector scans, and RAID state. Replace any failing drives promptly.
- Pause or wait for heavy background tasks (RAID rebuild, data scrubbing, indexing, snapshots) to finish and re-test.
- For many small files, expect lower throughput than with a single large file—test with a multi‑GB file to gauge true performance.
5. Firmware, Drivers, and Protocol Features
Outdated firmware or network drivers can cause stability and performance issues, and certain protocol features can materially affect throughput.
Solution:
- Update your NAS to the latest ADM firmware and apps via App Central. Check for updates regularly.
- Update your PC’s network adapter drivers and operating system.
- On modern Windows/macOS clients, use SMB3 for best performance. If supported by your environment, SMB Multichannel can improve throughput on multi‑path setups: About SMB Multichannel.
6. Antivirus, Firewall, and QoS
Real-time scanning of network shares and certain firewall or QoS features can throttle LAN traffic.
Solution:
- Temporarily disable real-time antivirus scanning and third‑party firewalls on the client to test. If speeds improve, add exclusions for your NAS shares and re‑enable protections.
- Check your router for QoS, parental controls, DPI, or traffic-shaping features that may slow LAN‑to‑LAN transfers. Disable them for testing.
7. Measure Correctly and Isolate the Issue
Copy dialogs often show MB/s (megabytes per second), while network specs use Mbps (megabits per second). 1 MB/s ≈ 8 Mbps, so a reading of 8 MB/s is about 64 Mbps.
Solution:
- Use a LAN throughput tool like iPerf3 to test pure network speed between your PC and NAS (or another PC). This helps separate network issues from disk or SMB overhead.
- Compare wired vs. Wi‑Fi results. For large transfers, always test over wired Ethernet.
If Speeds Are Still Poor
- Document your setup (NAS model, ADM version, switch/router model, cable types, link speeds, RAID state) and your test results (file size, MB/s shown, iPerf3 numbers).
- Contact Asustor Support with these details for tailored troubleshooting: Asustor Support.
