[tor-relays] Low observed bandwith

[Mario Costa]

Hi Roger,

Thank you for your answer, you and teor really helped me figure this out.

I set BW rate and burst to 10 MB/s and hope to get more traffic once the relay becomes guard for enough clients. Being on a dynamic IP I guess that every time the ISP changes my address and have to get a new guard flag, I’ll experience a drop in traffic.

-m 

> Il giorno 16 apr 2020, alle ore 16:22, Roger Dingledine <arma at torproject.org> ha scritto:
> 
> [Hi Mario! I wrote this draft and then stopped half-through, and then
> teor wrote a good response too. So I'm going to send it as-is, rather
> than quietly delete it, in case it helps reinforce some of the points
> that teor made.]
> 
> On Sat, Apr 11, 2020 at 02:55:59PM +0200, Mario Costa wrote:
>> I???m running a guard relay from my home connection on a Raspberry Pi 4.
> 
> Thanks for running a relay!
> 
>> My internet connection is 1000/100 Mbps, and I thought I???d allocate half of the upload bandwidth for the relay. Then I set RelayBandwidthRate to 10 MB/s, because I thought that Tor would upload 5 MB/s and download 5 MB/s.
> 
> Actually, a rate of 10mbytes/s means it will do up to 10mbytes/s upload
> and also up to 10mbytes/s download. That is, the rate setting applies to
> 'each way', not 'total for both'.
> 
>> However, the maximum observed bandwidth was always about 6 MB/s. I???d like to know what could cause this low observed bandwidth. I don???t think it???s the Raspberry Pi, because CPU usage is always low and it has a Gigabit connection to the router.
> 
> Answer #1: that 6mbytes/s is the most the relay has seen itself actually
> handle, in any ten-second period. That is, there was some ten second
> period over the past few days where the relay sent 60mbytes of actual
> traffic, and also some ten second period (doesn't have to be the same one)
> where it received 60mbytes of actual traffic.
> 
> So it isn't that the relay measured itself and found that it could only
> do 6mbytes/s. It's that the load from actual user traffic has reached that
> high, and so that's the number that it has seen itself do ("observed").
> 
> And that leads to the natural follow-up question of "Ok, but how come
> the user traffic only got that high? I could handle a lot more!"
> 
> And that's a harder question to answer, because it has to do with overall
> network load ("what all the Tor users together are trying to do right
> now"), and with load balancing across all the relays ("how much of that
> traffic gets sent toward your relay").
> 
> The simple answer is that random chance hasn't yet brought the combination
> of user flows to your relay at the right time to show it that it can
> do more.
> 
> But here, your 100mbit up limit looks like it could actually matter.
> The reason is that you can't push more than about 12 megabytes in a
> second, and that could impact whether you end up pushing more than 60
> megabytes in 10 seconds. I tried to construct a concrete scenario with
> numbers that add up, but I have so far failed to make a convincing one.
> So maybe 100mbit is sufficiently high that there aren't realistic
> scenarios where it will be a limitation. I'm not sure.
> 
> Hope this helps,
> --Roger
> 
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