2innocent
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number of users that can connect to raspberry 3b

Thu May 23, 2019 5:21 pm

Hello people, does any one know the maximum number of persons that can connect to raspberry 3b and if there are ways to increase that number. Thanks in advance

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mahjongg
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Re: number of users that can connect to raspberry 3b

Thu May 23, 2019 5:27 pm

Isn't five trillion people enough?
Oh, you meant at the same time..... :mrgreen: :lol:

connect how, Wifi, Ethernet, serial, bluetooth, I2C, SPI how?

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Re: number of users that can connect to raspberry 3b

Thu May 23, 2019 6:26 pm

At 20 connected sessions a PDP-11/70 running bsd 2.9 got pretty slow. A Pi3B+ is *lot* faster, but Raspbian has a lot more background stuff running.

How many people are *likely* to be connected at the same time? It also depends, of course, on what the people are doing. If they're all trying to compile a Linux kernel, it won't take many to bring the system to its knees. If they're all running trn or elm, it would probably handle a fairly large number.

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Re: number of users that can connect to raspberry 3b

Thu May 23, 2019 6:39 pm

Gets even worse if they are hitting a web server as the server application can have significant impact when the number of users go up...

As for increasing it - buy a Pi 3B+ or CM3+

If you want lots of users go Intel / AMD and Linux - more memory and more cores :oops:

By the way - welcome to the forum. We are not trying to put you off but please remember these wonderful cards are £35 and not the answer to everything computers can do.
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Heater
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Re: number of users that can connect to raspberry 3b

Thu May 23, 2019 7:15 pm

2innocent,

It's impossible to answer that question unless you give more information on what you require.

What kind of connection do you mean: To a web server (HTTP), terminal sessions(SSH), VNC connections, database connection, .... ?

What kind of work load do you expect those users to have?

How do you know you want to increase whatever limit it might be before you know what it is?

I'm sure Linux can hold thousands of network connections open at the same time if they are not doing anything. The limit will be on what service they are to provide. At some point you will run out of processing speed, memory space, storage access speed, network bandwidth.

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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:38 am

mahjongg wrote:
Thu May 23, 2019 5:27 pm
Isn't five trillion people enough?
Oh, you meant at the same time..... :mrgreen: :lol:

connect how, Wifi, Ethernet, serial, bluetooth, I2C, SPI how?
i am trying to istall moodle on raspberry pi so that students in a class can access educative contents and probably take tests by connecting their device through wifi connection to the pi, so i am wondering how many students should be able to connect at a time.

2innocent
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:39 am

Heater wrote:
Thu May 23, 2019 7:15 pm
2innocent,

It's impossible to answer that question unless you give more information on what you require.

What kind of connection do you mean: To a web server (HTTP), terminal sessions(SSH), VNC connections, database connection, .... ?

What kind of work load do you expect those users to have?

How do you know you want to increase whatever limit it might be before you know what it is?

I'm sure Linux can hold thousands of network connections open at the same time if they are not doing anything. The limit will be on what service they are to provide. At some point you will run out of processing speed, memory space, storage access speed, network bandwidth.
i am trying to istall moodle on raspberry pi so that students in a class can access educative contents and probably take tests by connecting their device through wifi connection to the pi, so i am wondering how many students should be able to connect at a time.
Top

2innocent
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:42 am

W. H. Heydt wrote:
Thu May 23, 2019 6:26 pm
At 20 connected sessions a PDP-11/70 running bsd 2.9 got pretty slow. A Pi3B+ is *lot* faster, but Raspbian has a lot more background stuff running.

How many people are *likely* to be connected at the same time? It also depends, of course, on what the people are doing. If they're all trying to compile a Linux kernel, it won't take many to bring the system to its knees. If they're all running trn or elm, it would probably handle a fairly large number.
it is basically for students to connect, learn and take tests

2innocent
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:47 am

mahjongg wrote:
Thu May 23, 2019 5:27 pm
Isn't five trillion people enough?
Oh, you meant at the same time..... :mrgreen: :lol:

connect how, Wifi, Ethernet, serial, bluetooth, I2C, SPI how?
yes dear, i mean at the same time. i am trying to set up moodle on raspberry pi for students to connect to and take tests in a class. the connection is via wifi. so m wondering how many students can connect at a time using RPi 3

2innocent
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:57 am

Andyroo wrote:
Thu May 23, 2019 6:39 pm
Gets even worse if they are hitting a web server as the server application can have significant impact when the number of users go up...

As for increasing it - buy a Pi 3B+ or CM3+

If you want lots of users go Intel / AMD and Linux - more memory and more cores :oops:

By the way - welcome to the forum. We are not trying to put you off but please remember these wonderful cards are £35 and not the answer to everything computers can do.
it is suppose to be an offline learning repository hence it shouldnt be hitting any web server. Thanks, i understand it has its limitations, just trying to be creative with what it can do.

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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 12:26 pm

If you are thinking of Moodlebox as your software then this gives you a guideline:
MoodleBox is built around a mini computer Raspberry Pi 3 Model B or Model B+. Its super light architecture enables to use it with 20 to max 30 users.

It is not designed to support big groups.
Taken from https://moodlebox.net/en/help/moodlebox ... any-users/
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mina
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 2:06 pm

2innocent wrote:
Fri May 24, 2019 8:39 am
i am trying to istall moodle on raspberry pi so that students in a class can access educative contents and probably take tests by connecting their device through wifi connection to the pi, so i am wondering how many students should be able to connect at a time.
Top
The WiFi is the limiting factor here. As already stated above, you can expect between 20-30 users connected simultaneously (see https://moodlebox.net/en/help/moodlebox ... any-users/)

Disclaimer: I'm the maintainer of MoodleBox.
Nicolas – Maintainer of MoodleBox, a Moodle server on Raspberry Pi

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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 3:36 pm

mina wrote:
Fri May 24, 2019 2:06 pm
2innocent wrote:
Fri May 24, 2019 8:39 am
i am trying to istall moodle on raspberry pi so that students in a class can access educative contents and probably take tests by connecting their device through wifi connection to the pi, so i am wondering how many students should be able to connect at a time.
Top
The WiFi is the limiting factor here. As already stated above, you can expect between 20-30 users connected simultaneously (see https://moodlebox.net/en/help/moodlebox ... any-users/)

Disclaimer: I'm the maintainer of MoodleBox.
Has this changed on the Pi3B+ with the faster wifi?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 3:46 pm

jamesh wrote:
Fri May 24, 2019 3:36 pm
mina wrote:
Fri May 24, 2019 2:06 pm
2innocent wrote:
Fri May 24, 2019 8:39 am
i am trying to istall moodle on raspberry pi so that students in a class can access educative contents and probably take tests by connecting their device through wifi connection to the pi, so i am wondering how many students should be able to connect at a time.
Top
The WiFi is the limiting factor here. As already stated above, you can expect between 20-30 users connected simultaneously (see https://moodlebox.net/en/help/moodlebox ... any-users/)

Disclaimer: I'm the maintainer of MoodleBox.
Has this changed on the Pi3B+ with the faster wifi?
Unfortunately no :( . The speed has changed, but NOT the number of users.
Nicolas – Maintainer of MoodleBox, a Moodle server on Raspberry Pi

jamesh
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 8:31 pm

mina wrote:
Fri May 24, 2019 3:46 pm
jamesh wrote:
Fri May 24, 2019 3:36 pm
mina wrote:
Fri May 24, 2019 2:06 pm


The WiFi is the limiting factor here. As already stated above, you can expect between 20-30 users connected simultaneously (see https://moodlebox.net/en/help/moodlebox ... any-users/)

Disclaimer: I'm the maintainer of MoodleBox.
Has this changed on the Pi3B+ with the faster wifi?
Unfortunately no :( . The speed has changed, but NOT the number of users.
Interesting, what do you think is the cause of the limitation?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 9:59 pm

jamesh wrote:
Fri May 24, 2019 8:31 pm
Interesting, what do you think is the cause of the limitation?
It's 100% guaranteed to be lack of RAM. Each user will take a chunk of RAM on the server. When that pushes your server over the 1GB limit (into swapping hell) you'll reach a practical limit.

The big iron I work on for my day job runs out at 480GB before swapping or paging anything to disk.
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 10:04 pm

DougieLawson wrote:
Fri May 24, 2019 9:59 pm
jamesh wrote:
Fri May 24, 2019 8:31 pm
Interesting, what do you think is the cause of the limitation?
It's 100% guaranteed to be lack of RAM. Each user will take a chunk of RAM on the server. When that pushes your server over the 1GB limit (into swapping hell) you'll reach a practical limit.

The big iron I work on for my day job runs out at 480GB before swapping or paging anything to disk.
Wonder if a fast disk and big swap space on it would let you push the limit up much...
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 10:20 pm

Andyroo wrote:
Fri May 24, 2019 10:04 pm
Wonder if a fast disk and big swap space on it would let you push the limit up much...
In an ideal world you never want your steady state working set to move out to any slow device. Before we could go super sized on mainframes the rule was 67% max. With the other 33% there for the mid-day peaks (in banking we got a peak around 11am and a second around 2pm - now in banking they get a massive peak between 11:30pm and 12:30am when folks check their phones to see if they've been paid).

You can swap to spinning things or solid-state spinning look-alike things but that will reduce the overall throughput for everyone when any ready-to-run process has to pause for a swapped page to come back from the USB device.
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 11:01 pm

I would hope that intermittent users could stand a page or two...

I know when we modelled the last Citrix system we ended up with role based workloads - upset some managers when we rated their workload as low impact and could be paged out compared to customer service staff :lol:

i Wonder if any regular moodle users have tried it?
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Re: number of users that can connect to raspberry 3b

Fri May 24, 2019 11:42 pm

It's kind of disturbing that, despite the huge improvement is CPU speed and memory that even a Pi represents over a PDP 11/70, the total number supportable concurrent users hasn't increased in 40 years.

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Re: number of users that can connect to raspberry 3b

Sat May 25, 2019 8:26 am

DougieLawson wrote:
Fri May 24, 2019 9:59 pm
jamesh wrote:
Fri May 24, 2019 8:31 pm
Interesting, what do you think is the cause of the limitation?
It's 100% guaranteed to be lack of RAM. Each user will take a chunk of RAM on the server. When that pushes your server over the 1GB limit (into swapping hell) you'll reach a practical limit.

The big iron I work on for my day job runs out at 480GB before swapping or paging anything to disk.
Are you saying that each new wifi connection take so much RAM that after 25 users the RPi freezes? Interesting (I thought myself it could be a wifi driver problem.)

I'll try to do some tests to see wether your assertion holds.
Nicolas – Maintainer of MoodleBox, a Moodle server on Raspberry Pi

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Re: number of users that can connect to raspberry 3b

Sat May 25, 2019 8:56 am

mina wrote:
Sat May 25, 2019 8:26 am
Are you saying that each new wifi connection take so much RAM that after 25 users the RPi freezes? Interesting (I thought myself it could be a wifi driver problem.)

I'll try to do some tests to see wether your assertion holds.
No, I'm saying you need to measure the base RAM usage when the system is booted and ready for use. Measure how much it increases for 1, 2, 5, 10, 15, 20 connected users. Then do some scrap paper maths to workout where the theoretical limit will be. Then do an empirical test to see how many users flood the system. You're aiming for 95% cpu busy on four cores and approx 67% RAM committed as the practical limits.
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Re: number of users that can connect to raspberry 3b

Sat May 25, 2019 10:52 am

DougieLawson wrote:
Sat May 25, 2019 8:56 am
mina wrote:
Sat May 25, 2019 8:26 am
Are you saying that each new wifi connection take so much RAM that after 25 users the RPi freezes? Interesting (I thought myself it could be a wifi driver problem.)

I'll try to do some tests to see wether your assertion holds.
No, I'm saying you need to measure the base RAM usage when the system is booted and ready for use. Measure how much it increases for 1, 2, 5, 10, 15, 20 connected users. Then do some scrap paper maths to workout where the theoretical limit will be. Then do an empirical test to see how many users flood the system. You're aiming for 95% cpu busy on four cores and approx 67% RAM committed as the practical limits.
I think you don't understand the use case: the device serves as a wifi AP and a web server, that's all. No user is logged in the RPi in production use.

Nginx and php-fpm are optimized so that memory is not a problem. Flooding the web server using ApacheBench shows that memory is not a problem: available memory remains at around 600M at any time, even with 100 concurrent http requests! Swap is never used.

The limitation I experience is uniquely caused by concurrent wifi connections to the AP (hostapd), and that's the reason I'm suspecting it's a wifi driver issue.

I'd be glad for any suggestion.
Nicolas – Maintainer of MoodleBox, a Moodle server on Raspberry Pi

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Re: number of users that can connect to raspberry 3b

Sat May 25, 2019 11:13 am

Wonder if a different WiFi dongle would help? Rather than the internal one try a USB connected one.

I know it defeats the ‘one box’ idea but does the same thing happen if you use an external AP and connect back to the Pi via Ethernet?
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Re: number of users that can connect to raspberry 3b

Sat May 25, 2019 11:42 am

Andyroo wrote:
Sat May 25, 2019 11:13 am
Wonder if a different WiFi dongle would help? Rather than the internal one try a USB connected one.

I know it defeats the ‘one box’ idea but does the same thing happen if you use an external AP and connect back to the Pi via Ethernet?
I'm sure that this would do the job, but as you say it'll defeats the 'one box' idea, which is absolutely a no-go for most of the (non tech savvy) users.
Nicolas – Maintainer of MoodleBox, a Moodle server on Raspberry Pi

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