Very slow download speeds on Ubuntu (compared to Windows)

[MPenguin]

I previously had Sabnzbd running on Windows 10. My connection maxes out at around 80 Mbps. I've been moving to an Ubuntu server on a NUC, and I noticed that Sabnzbd now has extremely slow download speeds.

TheSpeedtest from the command line on Ubuntu shows:

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Download: 79.58 Mbit/s
Upload: 37.52 Mbit/s

But Sabnzbd is only getting ~200 KB/s. It's setup the same as I had it on Windows, with the same servers. I've tried playing with the number of connections, but it makes no difference. What can I do to get back up to my fast download speeds?

Thanks.

[sander]

In SABnzbd's upper right corner, click on the wrench symbol ("Status and interface options"), then click on first tab Status, and therev click on the Refresh Arrow.

... what numbers do you get? Post them here.

[MPenguin]

This is running on an Intel NUC 10i5 with 32gb RAM and a 500gb NVME drive running Ubuntu Server 20.04.1 LTS

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System performance (Pystone) 304180 Intel(R) Core(TM) i5-1021…
Download folder speed 756.1 MB/s (/nas/downloads)
Complete folder speed 914.8 MB/s (/nas/complete)
Internet Bandwidth 2.7 MB/s (21.6 Mbps) 

Just tried the 100MB test download. My connection started at 1MB/s and then dwindled back down to ~200 KB/s.

[sander]

Your CPU and disks are fantastic (NVMe?), but your Internet is very slow: "Internet Bandwidth 2.7 MB/s (21.6 Mbps)".

Is that what you buy from your ISP? If not, solve that.

[MPenguin]

Your disks are fantastic (NVMe?), but your Internet is very slow: "Internet Bandwidth 2.7 MB/s (21.6 Mbps)".

Is that what you buy from your ISP? If not, solve that.

We pay for 100/50but we live quite a ways out of town, so we normally get about 80/40. This is what is shown by checking speedtest.net from the command line:

Testing download speed................................................................................
Download: 80.62 Mbit/s
Testing upload speed......................................................................................................
Upload: 38.83 Mbit/s

So why is Sabnzbd only seeing 21.6 Mbps when I should be getting ~80 Mbps?
There is no problem with the Internet. On my Win10 pc (same network, same router), I get the fastest speeds. It's only Sabnzbd on this Intel NUC that is slowing down.

[sander]

I don't know. On my Ubuntu both measurements match:

the speedtest CLI says

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     Server: Korton Group BV - Hoofddorp (id = 5124)
        ISP: CAIW Internet
    Latency:     3.71 ms   (0.18 ms jitter)
   Download:   173.86 Mbps (data used: 129.6 MB)                               
     Upload:   172.38 Mbps (data used: 89.0 MB)            

and SABnzbd Wrench says

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Internet Bandwidth 17.7 MB/s  (141.6 Mbps)

So they match

Oh, wait: at the moment you do the SABnzbd Wrench Speed test ... SAB is not download anything from Newsserver, I hope?

[MPenguin]

Correct, when I ran both the speedtest from the CLI and the wrench, I was not downloading anything else and there was no other traffic on the server.

Could this be an odd kernel issue? I'm on 5.4.

[MPenguin]

I just reran the diagnostics on my main machine using Windows 10 and got very comparable numbers to the NUC.

I'm now suspecting that something has changed since I hooked both the NUC and the Synology up to the network. Possibly also something with the port-forwarding settings.

EDIT: Not sure what changed. I unplugged the NUC and Syno from the internet, restarted my main pc, plugged both the NUC and Syno back in, and now speeds are back to normal. No clue. I'll keep an eye on this issue and see if it pops up again and if there is any pattern to it.