Syncthing Hub Design One Always On Device Keeps Every Device in Sync
Syncthing has no master device — but a setup with one always-on machine at the centre behaves like it does. This guide explains the hub design honestly: why it works, what to use as the hub, and where its limits are.
✍️ Technical Anshu🖥️ Windows / Linux / NAS⏱️ Planning guide, 10 minute read
🎥 See the hub based setup built from scratch in the full Syncthing server video
Technically, Syncthing is a mesh: every device syncs with every other device it meets, and no device is in charge. That is elegant, but real life is messier. Your laptop sleeps. Your phone leaves the house. If those two are your only devices, they can only sync during the hours both happen to be awake and online together. One always-on hub fixes the calendar problem — and this guide shows how to design around it properly.
The hub pattern — devices sync whenever they wake, the hub is always there
┌──────────────┐
│ HUB PC │ always on
Laptop ──────▶│ holds every │◀────── Phone
(sleeps, │ folder, │ (leaves the
travels) │ versioning │ house)
│ ON │
└──────────────┘
Rule: every device pairs WITH THE HUB.
Laptop and phone do not need to meet each other.
Illustrative diagram — the hub is a normal Syncthing device, just one that rarely sleeps
1
Why the Hub Pattern Works
Without a hub, sync is a meeting problem: two devices must be awake, online and able to reach each other at the same moment. With a hub, the problem disappears, because the hub is awake at 3 AM when your phone backs up its photos, and awake at noon when your laptop opens for work.
The phone uploads new photos to the hub at night. Done — the phone can sleep.
The laptop, opened in the morning, downloads them from the hub. It never needed to meet the phone.
You edit a document on the laptop at a client's office. It syncs up to the hub over the internet. The home PC already has it when you return.
The hub is also the natural home for file versioning, because it has the big disk and the always-on duty of keeping older copies.
2
Choosing the Hub Honestly
Almost any machine qualifies, but some qualify better:
An office or home desktop — the classic choice. On all day anyway, big internal disk, wired network.
A mini PC — the ideal choice. Sips power, silent, can run for months untouched. A used office mini PC is plenty.
A NAS or small Linux server — excellent if you already run one. Syncthing installs natively on most NAS platforms and every Linux distribution.
An old laptop — workable, with honest caveats: set it to never sleep, keep it plugged in, and remember its battery is aging while acting as a UPS. Remove or manage the battery if it starts swelling.
Your main travelling laptop — the poor choice. It is the device most often off, asleep or in a bag, so it makes a hub that is never there.
3
Pair Everything With the Hub, Not With Everything
In a three or four device setup, pair each device with the hub. Pairing the laptop directly with the phone as well is allowed and occasionally useful on the same LAN, but it is not required, and each extra pairing is one more relationship to understand when something looks wrong.
Hub pairs with laptop. Hub pairs with phone. Done — that is the whole map for most people.
Folders are shared from the hub outward, so there is one place where you check "who has this folder".
When you replace a device, you pair the new one with the hub, share the folders, and let it fill up. The hub is the source of truth for what "complete" means.
4
What the Hub Is Not
Keep the honest limits in view:
The hub is not a backup by itself. It holds a synced copy, and synced copies share the fate of the originals — deletion and corruption travel. Versioning on the hub and one separate offline copy are still needed for real backup.
The hub is a single point of waiting, not of failure. If it dies, no data is lost from the other devices; they keep their copies and can be paired anew. But nothing syncs until something replaces it.
The hub needs disk for everyone's everything. Size it for the full set of folders plus versioning history plus growth, or it will quietly fill up and stop syncing — Syncthing does warn when free space runs low, if anyone is watching.
🔴 The design rule in one line: the hub should be the machine you would miss least as a computer and notice most as an absence — boring, wired, always on, and with the biggest disk you own. Fancy is useless here; awake is everything.
🎥 Watch the Hub Setup Built in the Video
The full Syncthing server video builds this exact pattern — one always-on PC, a laptop and a phone, syncing in real time.
Yes, for documents and photos it is more than enough. Syncthing is light on CPU for typical office files. Very large first-time syncs and heavy hashing of huge video files will be slow on weak hardware, but steady daily sync is fine.
Should the hub use Receive Only folders?
For folders the hub only stores — like phone photos — Receive Only is exactly right. For working folders the hub's owner also edits, Send and Receive is correct. Folder type is per device, so the same folder can be Receive Only on the hub and Send and Receive on your laptop.
What if I have two always-on machines, at home and at the office?
Pair devices with both and share the folders with both. Syncthing handles multiple sources happily and will pull different pieces from each. Just keep versioning enabled on at least one of them, and be sure both have the disk space for the full set.
This guide is part of the Syncthing series by Technical Anshu • Watch the main setup video for the full live build 🙏