sync speed is decreasing over hours..

dear all,

I would like to ask, why my sync speed is decreasing over hours… refeering to “Why is synchronization between two devices so slow?” and “FAQ — Syncthing documentation” I did not find a hint…

I sync from MAC (M2, 32 Gig) to a raspberry Pi 5 (8 Gig). after some hours, the speed goes down from (just now as example) “2,21 MiB/s (3,1 GiB)” to at about 200…500K. When I restart both sides via WEB-insterface, the speed immediately goes up again to previous level.

Background: on both sides the disks are USB-3-connected. Connection between the 2 computers is WLAN.

versions raspberryPi: syncthing v1.27.3, Linux (64-bit ARM)

  • OS “Debian GNU/Linux 12 (bookworm)”
  • HW Raspberry Pi 5 Model B Rev 1.0

MAC: syncthing v1.27.2, macOS (64-bit ARM)

  • OS Ventura, 13.6.4
  • HW Apple M2 Pro

history on “raspi-side” I recently switched from raspi 4B → raspi 5 (see above). because of many files (~2…3 TB) I keept the files on “raspi-side” and now (try to) re-sync …

any ideas, hints? thanks in advance jürgen

I have heard this but not seen it nailed down. Taking CPU, block and heap profiles before and after might be helpful.

Also watch out for the CPU temperature on the raspi. If heavy hashing or encryption is involved, it might be throttling down because it gets hotter by the minute.


The SD card of the pi might also throttle. I know you’re syncing to an USB3 drive, but syncthings database is most likely still on your rootfs.

I think, you’re right … it might be NOT a syncthing problem…

(I forgot to mention: I boot the raspi from usb disk, data is on a different disk, not the same, so hopefully the SD-card should not be involved in my case …)

temperatur: values : (last 2 days)

  • 54.3°C … 67.5°C
  • 55.4°C … 68.6°C

→ might this be a problem? (I did not find reliable values for “too high” temperatures… found somthing ~80°C, but from my point of view -gut feeling- thats MUCH too high … what do you think?

– I stopped syncthing and tried to transfer my data from mac to raspi via “rsync -av…”.

→ I found the same reaction: it started quickly, slowed down over night… so it could be a “local raspi-problen”

Depends on if those numbers are when the system is fully loaded or when the system is idle.

Is there any active cooling in your RPi 5 rig?

At least a few of the past Raspberry Pi models (including the RPi 5) have thermal CPU throttling with two thresholds at 80°C and 85°C.

What’s the capacity of the power supply for the RPi?

Is the USB drive holding the data self-powered or has an external power supply?

the power suppply offers 27W, the usb sys-disks is directly, the data disks are connected via powered-usb hub.

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.