Download Slowdown Issue (A Different One I Think)

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hypersucker
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Download Slowdown Issue (A Different One I Think)

Post by hypersucker » February 14th, 2020, 6:50 pm

I assume my issue arises from either a network or a disk throughput bottleneck and I need pointers on where to look and how to solve it.

When I add 2ish jobs to the queue (sometimes 4-5 work too) all is well in SABNZBd world and my down speed is a constant 125/130MB/s.

However, when more jobs are added, the speed drops to 40-60MB/s. It starts when multiple jobs are downloading at once (simultaneously) AND 2 or more jobs are direct unpacking and unpacking and repairing at the same time.

SABNZBd downloads to a fast SSD, then unloads finished stuff to a NAS networked via gigabit ethernet that does around 120MB/s steadily.

It looks like the SSD seems to have issues with all the combined activity. Is that probable? And if so, can I tweak this somehow so SABNZBd performs well like when jobs are added one after the other manually?

I tested adding new jobs just before the current one finishes downloading and the one before that is just about to finish unpacking to the network drive and repeated that for about 20 jobs all the while the speed never dropped below 120MB/s. When I added the same 20 jobs at once, after the 4th or 5th job, the down speed dropped to about 40MB/s and stayed there.

I cant see anything relevant in the log and I’m unsure where exactly the bottleneck lies.

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safihre
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Re: Download Slowdown Issue (A Different One I Think)

Post by safihre » February 16th, 2020, 11:32 am

I think you are just running into the limitations of Sabnzbd. The program is written in Python, which is a great language to learn programming and do simple tasks, however, it's mostly single threaded. So when it is focusing on 1 task (thread) it will basically ignored the rest. This is very much an over simplification, but that's kind of what happens.. We have added a lot of tricks to sabnzbd to let it still perform reasonable with multiple tasks, but when your download speed is 100MB/s it just can't handle :(

I think you should try nzbget, it's a bit less user friendly but it's written in C++ and can seamlessly handle everything at once :)

hypersucker
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Re: Download Slowdown Issue (A Different One I Think)

Post by hypersucker » February 16th, 2020, 7:03 pm

I dont like the nzbget interface. But every now and then I use it anyway. No worries, I usually dont have that high a workload (just have to quickly reget a couple of hundred things) and SABNZBd works just fine for now.

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