Network speed of NAS only hitting 40MB/s

Fods · December 18, 2025, 12:38pm

I’m having a weird issues and I’m struggling to troubleshoot.
I recently rebooted my nas and started to transfer my file, from a PC to the nas via the SMB share

For some reason when i copy from the PC to the nas i’m only getting around 40Mb/s
Both the PC and NAS have a 1GB network card and they seem to be connected with to the network with the right 1000Mb/s
The PC can hit the 1Gb/s my internet gives me so I’m ruling that out.

Basic nas specs:

i5-8400
32GB ddr 3200
Version 25.04

To help troubleshoot i did a Iperf3 is giving me this result with the NAS 227 being the nas and 10 being my PC

Server listening on 5201 (test #1)

-----------------------------------------------------------

Accepted connection from 192.168.1.10, port 54680

[ 5] local 192.168.1.227 port 5201 connected to 192.168.1.10 port 54681

[ ID] Interval Transfer Bitrate

[ 5] 0.00-1.00 sec 39.2 MBytes 329 Mbits/sec

[ 5] 1.00-2.00 sec 38.8 MBytes 326 Mbits/sec

[ 5] 2.00-3.00 sec 39.2 MBytes 329 Mbits/sec

[ 5] 3.00-4.00 sec 38.9 MBytes 326 Mbits/sec

[ 5] 4.00-5.00 sec 39.2 MBytes 329 Mbits/sec

[ 5] 5.00-6.00 sec 39.2 MBytes 329 Mbits/sec

[ 5] 6.00-7.00 sec 39.0 MBytes 327 Mbits/sec

[ 5] 7.00-8.00 sec 38.9 MBytes 326 Mbits/sec

[ 5] 8.00-9.00 sec 38.7 MBytes 324 Mbits/sec

[ 5] 9.00-10.00 sec 39.1 MBytes 328 Mbits/sec

[ 5] 10.00-10.01 sec 237 KBytes 333 Mbits/sec

- - - - - - - - - - - - - - - - - - - - - - - - -

[ ID] Interval Transfer Bitrate

[ 5] 0.00-10.01 sec 390 MBytes 327 Mbits/sec receiver

The settings for my interface are looking like this

Settings for enp3s0:

Supported ports: [ TP MII ]

Supported link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Full

Supported pause frame use: Symmetric Receive-only

Supports auto-negotiation: Yes

Supported FEC modes: Not reported

Advertised link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Full

Advertised pause frame use: Symmetric Receive-only

Advertised auto-negotiation: Yes

Advertised FEC modes: Not reported

Link partner advertised link modes: 10baseT/Half 10baseT/Full

100baseT/Half 100baseT/Full

1000baseT/Full

Link partner advertised pause frame use: No

Link partner advertised auto-negotiation: Yes

Link partner advertised FEC modes: Not reported

Speed: 1000Mb/s

Duplex: Full

Auto-negotiation: on

master-slave cfg: preferred slave

master-slave status: slave

Port: Twisted Pair

PHYAD: 0

Transceiver: external

MDI-X: Unknown

Supports Wake-on: pumbg

Wake-on: d

Link detected: yes

Does anybody have an idea on what to look for?
Thank you kindly!

Farout · December 18, 2025, 12:43pm

What is your pool layout, and is this a new problem only since the reboot ?
How full is your pool ?

Fods · December 18, 2025, 12:52pm

Good question. it is indeed a new pool.
Sorry i’m a novice to this. Please tell me what info you need. I’m not sure if the below is the right info

pool: LegendVille
state: ONLINE
status: Some supported and requested features are not enabled on the pool.
The pool can still be used, but some features are unavailable.
action: Enable all features using ‘zpool upgrade’. Once this is done,
the pool may no longer be accessible by software that does not support
the features. See zpool-features(7) for details.
config:

    NAME                                      STATE     READ WRITE CKSUM
    LegendVille                               ONLINE       0     0     0
      mirror-0                                ONLINE       0     0     0
        3acfa254-d263-4401-89c7-5d241c35e429  ONLINE       0     0     0
        9b1b1137-2a75-4100-aa75-8a5b6673d936  ONLINE       0     0     0

errors: No known data errors

pool: boot-pool
state: ONLINE
status: Some supported and requested features are not enabled on the pool.
The pool can still be used, but some features are unavailable.
action: Enable all features using ‘zpool upgrade’. Once this is done,
the pool may no longer be accessible by software that does not support
the features. See zpool-features(7) for details.
scan: scrub repaired 0B in 00:00:41 with 0 errors on Tue Dec 16 03:45:42 2025
config:

    NAME        STATE     READ WRITE CKSUM
    boot-pool   ONLINE       0     0     0
      sdc3      ONLINE       0     0     0

Farout · December 18, 2025, 12:56pm

How are the discs connected and whats the exact model of the drives ?
Are they directly plugged into the motherboards SATA ports or through some adapter or HBA ?
Is this virtualized or bare metal ?

HBAs and adapter cards can overheat and throttle throughput
SMR drives have very bad write speeds when used with ZFS

Fods · December 18, 2025, 1:01pm

1 is a seagate ironwolf, the other is an ironwolf pro. Both 8TB

**Disk Type:**HDD

Description:

**Model:**ST8000NT001-3LZ101

**Transfer Mode:**Auto

**Rotation Rate (RPM):**7200

**HDD Standby:**Always On

**Adv. Power Management:**Disabled

**Enable S.M.A.R.T.:**Yes

**Disk Type:**HDD

Description:

**Model:**ST8000VN004-3CP101

**Transfer Mode:**Auto

**Rotation Rate (RPM):**7200

**HDD Standby:**Always On

**Adv. Power Management:**Disabled

**Enable S.M.A.R.T.:**Yes

I believe they are both connected through SATA on the motherboard. Nothing funky. I’ll obviously go and check to verify the physical side of things

Thanks already for helping Farout!

TheColin21 · December 18, 2025, 1:06pm

It can’t be the pool when iperf is already slow. There’s something wrong with the network.
Can you do iperf tests with these two devices and a third one to find out which device causes the low bandwidth?

Fods · December 18, 2025, 1:09pm

i don’t have a 3rd device yet i can download at 1GB/s fibre from the internet with the PC.

If i do a speed test using the “open speed test” app on the NAS i get the same 40Mb/s max download. So i do think it’s the nas that is the problem not the PC nor the network (tried different ports on the 24 ubiquiti switch it’s on)

Fods · December 18, 2025, 1:10pm

I’m going to try different cables again to rule it out
Different cable. same issue. Cable sustains the 1GB on the PC as well so it’s not that

TheColin21 · December 18, 2025, 1:17pm

Ah yes I overlooked that. You can also try a speed test on the NAS? (for example by download hetzner speed test files https://fsn1-speed.hetzner.com/)?

As you said that you have a ubiquiti switch - if you have a dedicated Unifi console you can also run iperf3 there via ssh.

Running iperf3 bidirectionally might also be interesting.

Fods · December 18, 2025, 1:25pm

Wow you are onto something.

Iperf3 from the nas to the ubiquiti gateway being the server get the full speed.
Accepted connection from 192.168.1.227, port 38960
[ 5] local 192.168.1.1 port 5201 connected to 192.168.1.227 port 38970
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.00 sec 108 MBytes 903 Mbits/sec
[ 5] 1.00-2.00 sec 108 MBytes 910 Mbits/sec
[ 5] 2.00-3.00 sec 109 MBytes 917 Mbits/sec
[ 5] 3.00-4.00 sec 109 MBytes 913 Mbits/sec
[ 5] 4.00-5.00 sec 109 MBytes 914 Mbits/sec
[ 5] 5.00-6.00 sec 109 MBytes 914 Mbits/sec
[ 5] 6.00-7.00 sec 109 MBytes 916 Mbits/sec
[ 5] 7.00-8.00 sec 109 MBytes 915 Mbits/sec
[ 5] 8.00-9.00 sec 109 MBytes 916 Mbits/sec
[ 5] 9.00-10.00 sec 109 MBytes 918 Mbits/sec

[ ID] Interval Transfer Bitrate
[ 5] 0.00-10.00 sec 1.06 GBytes 914 Mbits/sec

Fods · December 18, 2025, 1:27pm

Gents thank you so much. It’s not the NAS its the PC.

Iperf from PC to unifi gateway
Accepted connection from 192.168.1.227, port 38960
[ 5] local 192.168.1.1 port 5201 connected to 192.168.1.227 port 38970
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.00 sec 108 MBytes 903 Mbits/sec
[ 5] 1.00-2.00 sec 108 MBytes 910 Mbits/sec
[ 5] 2.00-3.00 sec 109 MBytes 917 Mbits/sec
[ 5] 3.00-4.00 sec 109 MBytes 913 Mbits/sec
[ 5] 4.00-5.00 sec 109 MBytes 914 Mbits/sec
[ 5] 5.00-6.00 sec 109 MBytes 914 Mbits/sec
[ 5] 6.00-7.00 sec 109 MBytes 916 Mbits/sec
[ 5] 7.00-8.00 sec 109 MBytes 915 Mbits/sec
[ 5] 8.00-9.00 sec 109 MBytes 916 Mbits/sec
[ 5] 9.00-10.00 sec 109 MBytes 918 Mbits/sec

[ ID] Interval Transfer Bitrate
[ 5] 0.00-10.00 sec 1.06 GBytes 914 Mbits/sec

Thank you. Wrong forum now Thank you so much for helping!

TheColin21 · December 18, 2025, 1:28pm

I think you posted the wrong numbers for the PC but I’m happy I could help nonetheless.

Fods · December 18, 2025, 1:29pm

Yes you are right

C:\Users\stijn\Downloads>iperf3.exe -c 192.168.1.1
Connecting to host 192.168.1.1, port 5201
[ 4] local 192.168.1.10 port 62965 connected to 192.168.1.1 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 39.4 MBytes 330 Mbits/sec
[ 4] 1.00-2.00 sec 38.4 MBytes 323 Mbits/sec
[ 4] 2.00-3.00 sec 38.2 MBytes 320 Mbits/sec
[ 4] 3.00-4.00 sec 39.4 MBytes 330 Mbits/sec
[ 4] 4.00-5.00 sec 39.5 MBytes 331 Mbits/sec
[ 4] 5.00-6.00 sec 39.5 MBytes 332 Mbits/sec
[ 4] 6.00-7.00 sec 39.8 MBytes 333 Mbits/sec
[ 4] 7.00-8.00 sec 38.6 MBytes 324 Mbits/sec
[ 4] 8.00-9.00 sec 38.9 MBytes 326 Mbits/sec
[ 4] 9.00-10.00 sec 39.5 MBytes 330 Mbits/sec

[ ID] Interval Transfer Bandwidth
[ 4] 0.00-10.00 sec 391 MBytes 328 Mbits/sec sender
[ 4] 0.00-10.00 sec 391 MBytes 328 Mbits/sec receiver

iperf Done.