Slow Sync - Desperate - Need Help

Hi :slight_smile:


  • I’m experiencing a very slow sync since a while (only “One” textfile of “50kb” in "2-5"sec), although bigger files are sync way faster. Good speed. Couldn’t figure out what to do and reached a point where i would have to start getting a degree as a network admin first (it feels). → I’m desperate, and hope to find support by stronger souls here.


  • PC: Windows 11 (syncthing v1.25.0 “Gold Grasshopper”)
  • Phone: Android 13 Samsung Galaxy S20 FE (syncthing v1.23.7)
  • Router: FritzBox Cable 6660 (FRITZ!OS: 7.57)


  • The PC is connected to the FritzBox with a LAN cable (into the LAN1 slot of the router).
    • Performance of CPU is <5% while syncing
  • The Phone is connected to the router with WiFi 6, 2.5GHz.
    • Performance of CPU is 0% while syncing

Situation at the moment:

  • Both Devices (PC and Phone) are connected
    • and a folder is set up as “shared”
      • The folder has only textfiles (25.000).
  • Connection is via TCP LAN (Phone:, PC:
  • Compression is off, on both devices

PC Settings:

  • Windows 10: In a Private Network (before it was Public, but speed didnt change with beeing in a private one)
  • Syncthing: adress for sync protocol: default
  • Syncthing: data rate limit: 0
  • Syncthing: NAT: off (was on before, no change, its the same speed)
  • Syncthing: local search: on
  • Syncthing: global search: on (was off before, no change, its the same speed)
    • server for global search: default
  • Syncthing: relay: off

Phone Settings:

  • same as PC

PC Log:

  • 2023/11/02 09:46:26 INFO: Single thread SHA256 performance is 2082 MB/s using crypto/sha256 (2059 MB/s using minio/sha256-simd).
  • 2023/11/02 09:46:27 INFO: Hashing performance is 1318.80 MB/s
  • 2023/11/02 09:46:27 INFO: Overall send rate is unlimited, receive rate is unlimited
  • 2023/11/02 09:46:27 INFO: Using discovery mechanism: global discovery server https ://…
  • 2023/11/02 09:46:27 INFO: Using discovery mechanism: global discovery server https ://…
  • 2023/11/02 09:46:27 INFO: Using discovery mechanism: global discovery server https ://…
  • 2023/11/02 09:46:27 INFO: Using discovery mechanism: IPv4 local broadcast discovery on port 21027
  • 2023/11/02 09:46:27 INFO: Using discovery mechanism: IPv6 local multicast discovery on address … …
  • 2023/11/02 09:46:27 INFO: QUIC listener ([::]:22000) starting
  • 2023/11/02 09:46:27 INFO: TCP listener ([::]:22000) starting …
  • 2023/11/02 09:47:11 INFO: Established secure connection to … at…-…
  • 2023/11/02 09:47:11 INFO: Device … client is “syncthing v1.23.7” named “…” at…-…


  • I was reading so much that opening the ports on the windows machine didn’t change anything.
    • Also, i am overwelmed by the settings and options and adresses and numbers… its too much for me.
      • internal ports, external ports, routersettings, pc settings, and on and on.

Android sync will be slow regardless of the actual file size due to how the OS accesses files. There is no workaround for this apart from still using Android 10 or older.

1 Like

I will check that today with another Laptop. Thats good to know, thanks :slight_smile:

Your Android sync should not be annoyingly slow. I synchronize about 3 GB per day and it takes less than 4 minutes. I back up to my PC from my cell all of my SMS text messages which are several gigabytes and it flows pretty quickly between my cell phone and my laptop.

I think I saw that your connecting via TCP Lan which is what you want for the best performance. Can you check if the packets are going directly from PC to phone and not routing through your router via UPnP?

As a quick test you can always substitute the IP address for your laptop on the cell phone rather than using dynamic and see if by pointing it directly to the PC that needs to sync to if the speed improves.

This should not be necessary but you could use it as a process of elimination.

You can also run a bandwidth performance test between your cell phone and the PC using iperf. It measures throughput between two Network nodes and should give you an accurate measurement if you test it in both directions.

There is an iperf2 app in Google Play. It runs on Linux and Windows too. You should give you much better bandwidth as a verification that you don’t have a communication problem between your cell phone and the server.

If you prefer I prefer three there is a program called pingtools in the Android store that supports iperf3.

Iperf2 and iperf3 are not compatible with each other so they must run the same version on both sides.

Is the target Syncthing folder on your Samsung Galaxy S20 FE on the internal storage or a SD card?

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