NAS transfer speed is only a few tens of MB/s? Don't blame the hard drive for now, check these four places

Gigabit LAN, the theoretical transfer speed can reach 125MB/s, but in reality, it only runs 60MB/s or even slower - the file is obviously in the NAS, and it takes half a day to copy a small movie.

most of the time, it's not a NAS performance issue, but rather a link in the network link that is holding it back.

1. Measure the speed first and locate which section of the bottleneck

before troubleshooting, run it with iPerf or NAS's built-in speed test tool confirm the direction of the problem:

Judgment Criteria:

 fast direct connection speed (110MB/s+) → router or switch bottleneck Slow direct connection (<80MB/s) → NAS issues (NIC, LAN cable, configuration) NAS is fast locally, slow across networks → network link issues NAS is also slow locally → hard drive I/O bottleneck 

2. Troubleshooting 1: Network card rate negotiation problem (most common)

NAS If the NIC and router/switch port fail to negotiate, it will be downgraded to 100Mbps or half-duplex, and it will instantly become a "fake gigabit".

Investigation method (taking Synology as an example):

DSM → Control Panel → Network → LAN → Click Edit

view speed and duplex mode:

This is where the problem →
• Auto is common
• Gigabit Full Duplex (1000Mbps Full Duplex) → correct

Repair Method:

1. manually specified as 1000Mbps full-duplex both on the NAS and router side
2. if only one end can set it up, the other side keeps Auto negotiated
3. save the modification and restart the network service

Why is automatic negotiation problematic?
some low-end routers have poor network card compatibility, and the negotiation becomes 100Mbps half-duplex during automatic negotiation, and the speed can be increased by 5~10 times after manual designation.

3. Investigation 2: The network cable is not up to standard

this is the most overlooked link. The network cable looks good on the outside, but the inside may be aged or cut corners.

Identification Method:

Quick Judgment:

1. look at the network cable skin labeling, is it CAT5 or CAT5e
2. feel the thickness of the wire core, CAT5 is as thin as a toothpick, and CAT6 is obviously thicker
3. find a network cable that is known to be normal and test it

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tip: After network cable exceeds 50 meters, even a qualified CAT6 cable will slow down due to signal attenuation. CAT6a and above specifications are recommended for long-distance cabling.

4. Troubleshooting 3: Insufficient bandwidth of the router/switch backplane

router refers to each port independent gigabit, but when multiple devices are transmitting at the same time, the total bandwidth is limited by the CPU or switching chip , and there will be a race to slow down.

Typical Scenarios:

• NAS Normal speed when transferring to PC A
• at the same time, the NAS transmits another task to PC B, and both run at the same time, both of which are reduced to 50MB/s

Solution:

recommended switch for testing: TP-Link SG108E (8-port Gigbit, support port aggregation, about 150 yuan), NAS and computer are connected to this switch to test whether it returns to full speed.

5. Troubleshooting 4: SMB Protocol Version and Configuration Issues

Synology DSM 7.x disables SMBv1 by default and restricts some old protocol optimization options, Windows 10/11 may still be using SMBv2 by default but not enabling high-traffic optimization.

check Windows side SMB settings (Admin PowerShell):

# View the current SMB protocol version Get-SmbConnection # Enforce SMBv3 (Fastest) Set-SmbClientConfiguration -RequireEncryption $True 

optimize Samba performance on the Synology side:

DSM → Control Panel → File Services → SMB → Advanced Settings, check

 Enable SMB 3.0 multichannel (if both your router and PC support it) ☑ Enable transit encryption (NTLMv2 authentication) ☑ Maximum protocol version: SMB3 

Measured Comparison (Synology DS220+ + Gigabit Network):

6. Advanced: Use iPerf3 to accurately test the network speed limit

installed iPerf3 on both NAS and computer, and measured the maximum speed that the network can actually run

# NAS side (SSH in) as a server iperf3 -s # The computer side is the client and initiates the test iperf3 -c  -R 

results:

• rate > 940Mbps (about 118MB/s) → network link is fine, the problem is in the hard disk I/O
• rate is basically normal → 700~900Mbps, but there may be negotiation or interference
• rate < 600Mbps → Obvious bottlenecks in network cards, network cables, or switches