MrGlasspoole
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Joined: Sat Dec 09, 2017 12:24 am

Pi Zero timeserver capability

Thu May 24, 2018 1:04 pm

I did build a DCF77 timeserver with a Arduino and a Pi Zero.
The Arduino receives and decodes the time signal and sends it over serial to the Zero.
The Zero has a USB network adapter.

Everything works, but i wonder if the Zero has enough power.
Somebody has a rough idea how many network devices a Zero can serve?

Sure the Zero is headless and has no GUI.

hippy
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Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Pi Zero timeserver capability

Thu May 24, 2018 1:12 pm

MrGlasspoole wrote:
Thu May 24, 2018 1:04 pm
Somebody has a rough idea how many network devices a Zero can serve?
Potentially an infinite number of devices though it may be fewer depending on how those devices need to be served, the mechanism required to do that serving.

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B.Goode
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Location: UK

Re: Pi Zero timeserver capability

Thu May 24, 2018 2:20 pm

Some requests for information, to help you or other volunteers home in on an answer.

To distribute the time over the network to your user community, what technology or protocol are you using as the server on the RPi?

How large is the community of potential clients needing a time service?

What is the likely refresh rate for those clients - this will allow you to deduce how many simultaneous connections to the server you need to be able to handle.


(Which is a long-winded way of saying "I don't know". But maybe this isn't a common application for an RPiZero so maybe noone else will know either?)

MrGlasspoole
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Re: Pi Zero timeserver capability

Thu May 24, 2018 2:52 pm

Yes i know this is something nobody can really answer.
But i want to get a idea. This is just a home network and maybe someday 50 devices.

I did look around and for example this one:
https://www.meinbergglobal.com/english/ ... system.htm

AMD Geode LX 800 (500 MHz, 128 KB L2 cache)
Main Memory: onboard 256 MByte
GNU/Linux 4.x

The description says:
With several thousand NTP requests per second (depending on the installed CPU module), the system is able to provide time for hundreds and thousands of NTP clients.

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B.Goode
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Location: UK

Re: Pi Zero timeserver capability

Thu May 24, 2018 4:32 pm

Benchmarks and comparisons are slippery things, especially when looking at hardware with different instruction sets. But superficially your little RPiZero has twice the ram and double the CPU speed of the sample you cite.

So I doubt it can perform worse.

I don't think 50 clients making ocasional NTP requests is going to have much impact. (But it depends in part on how frequently the clients seek an update.)

Do you have anything to lose from a 'try it and see' approach? Find as many NTP client systems as you can, and configure them to do updates/lookups against your server as aggressively as you dare. Then check the system and network performance.

If it copes with an aggressive workload, it should be fine with a more normal pattern of use?

epoch1970
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Re: Pi Zero timeserver capability

Thu May 24, 2018 5:07 pm

I used to run Geodes of this type (PCEngines Alix), believe me the oldest Pi wipes the floor with a Geode.
If your service is NTP on a LAN there is no way your Pi will be hit by hundreds of requests/sec.
Besides, set NTP to send time via network broadcasts on the LAN, clients to listen to broadcasts, and you'll get 0 hits/sec.

To me the issue will be elsewhere. Because the Pi has no RTC clock, upon reboot...
- ... The server can change date by a large amount. NTPd doesn't like that, linux doesn't like that. There are conditions where the ntpd server will go poof right at the moment it becomes usable for clients. Personally to keep ntpd in check I use the watchdog program.
- ... The server can change date incrementally, for a long time (days or more). Everybody will have a slightly wrong date, or will be using the backup Internet time sources you've chosen. So much for running a perfectly good stratum-1 source. Personally to avoid this I run htpdate at boot (and watchdog runs it if the server went down) in order to step the clock close enough to the exact date for a fast sync.

I, for one, remember posting a few messages on these issues, look around the forums.
"S'il n'y a pas de solution, c'est qu'il n'y a pas de problème." Les Shadoks, J. Rouxel

MrGlasspoole
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Joined: Sat Dec 09, 2017 12:24 am

Re: Pi Zero timeserver capability

Thu May 24, 2018 5:37 pm

@epoch1970, sure i will add a RTC for boot times that the clients don't get the wrong time.

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