How does peer to peer download distribution works on syncthing

Hey All! :slight_smile: I searched this topic on the forum but didn’t find a specific awnser

I have a network on people working on the wame sync file. Some computers are together on the same lan network, others are working from different places in france

I am a bit lost regarding who exchanges data with who so here are some questions somehow related to each other :

  • If every file is on one computer A that shared the folder with all the others like B and C, do everybody exchanges with only this computer A or they (B and C) also exchange between them as long as computer A is online?
  • If yes what happens if A goes offline, can B and C computers sync without adding each other if they share the same sync?
  • Otherwise, do I need B and C to add each other, and do they also have to add each other to the sync for them to exchange this folder without A?
  • Are they prompted to add each other or to add this folder sync if they don’t add A as an introducer, as long as they share the sync?
  • When I add a computer as an introducer, does it mean that when people are adding the sync without knowing me they will be prompted about me and the sync (and that if they don’t accept, they can’t get files from me). Is there any other case where they will be prompted new computers without anybody setting a pc as an introducer.
  • Is it good practice to ask everyone to add pc A as an introducer and is it the only way to achieve a truly decentralized peer to peer network. Will they be prompted with a looooot of requests. Can it be achieved without using the introducer feature
  • If I have lots of computers added to the same sync, does it help with ditributing data and tranfer speed

My ideal is to kind of be able to let everyone get data from any computer sharing the folder, lan or internet, but without the need for them to add each other. Is it a behaviour syncthing can have?


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Devices will only sync with devices they’re connected to, and are sharing the same folders with. If B and C are not connected and not sharing the folder between each other, they will only sync with A. In this scenario, A must be online to sync.

If all of A, B and C are connected and all sharing a folder, they are all equals and will sync as long as two are online.

There is a section in the documentation about the Introducer feature. Read through this and come back if you have further questions, but it does sound like it’s suited to your use case.

Having more online devices helps improve syncing speed.

How many devices are you thinking about specifically? I believe connecting all of them together should be fine as long as the number is ~20 or lower. If it’s a much higher number though, you may encounter performance issues (depending, of course, on the hardware and connection speed and quality).

There can be exceptions though, e.g. I don’t usually connect mobile devices with many others, as trying to maintain all those connections can lead to battery drain, and I also do the same with devices that have very weak hardware, as they struggle to run Syncthing already. The same applies to devices located on very slow networks, etc.

Thanks for your help! I was thinking to sync about 10-15 people max. To slim down connexions i may ask only key computers with access to more files to add the server as an introducer then

Also, do you agree that adding a server as an introducer may ask a lot more from your computer and internet connexion so it’s best do to it only if the computer is powerful and with good connexion?

The Introducer feature simply means that the device’s shares and connected devices will be shared automatically. It bears no additional load just because it’s an Introducer. Unless it’s a low-powered device, 10-15 peers shouldn’t be a problem.

Ok thanks a lot! Graphically it means that devices adding the introducer will automatically be prompted my computer while my computer will not need to accept requests from new peers added by that computer, is that right?

Neither your device or other devices will receive a prompt - the process is automatic.

This is weird because each person adding the actual original server receives a prompt to add as a know computer AND and prompt to add the folder to share from any computer that set the orîginal computer as an introducer

However, computers adding it as an introducer indeed receives no prompt when one of those computers adds it

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