Understanding syncthing resync interval


I’m finding syncthing very beneficial to synchronize a my laptop dev machine with my faster desktop machine so when I get home I can switch to using my desktop machine and have the directory contain exactly what was on the laptop. I am however running into a few bothersome issues. First is that syncthing seems to be keeping the cpu constantly busy. I can actually hear my CPU fan spinning at a higher rate. Right now, according to the web UI, it’s running at 48% and that’s on a relatively new i5 (i5-4690).

The directory that I’m trying to sync is about 66GB, so fairly large. I’m also using the syncthing-inotify to try and reduce the work required by rescans.

So (finally) on to my questions.

  1. Is it feasible to sync directories of this size? Are others sync’ing larger directories?
  2. Do I need to adjust the rescan interval based on the size of the directory I’m trying to synchronize? Is syncthing smart enough not to start from the beginning if it’s rescan interval expires but it has not completed the previous scan?
  3. How can I understand what syncthing is doing when the cpu usage is high?
  4. If I run syncthing as my normal user, and my directories contain files created by root, will syncthing be able to skip over those files and sync all the rest? Right now it seems that it bails out when it can’t synchronize a file.

Thanks in advance, Pico


Yes. You should set a higher interval for larger folders, and especially if you are using inotify. That said, the configured interval is essentially the time between the end of one scan until the start of the next.

Ideally it should be visible in the GUI - “scanning” or “syncing” on a folder for example. If not, there are various trace options, but it’s kind of developery and nasty. Also, note that loading (and having up) the GUI adds some CPU usage. There are situations where a sync fails and is continuously retried that drives up CPU usage - if this is the case, you have visible error messages in the UI.

Syncthing will complain about files it fails to update, sync all other files, and retry a minute later. This may be one of those things that drive up your CPU usage, though.

Files owned by root aren’t a large problem by itself - if they are still readable they can be synced to other devices, if they are in a directory owned by you they can be replaced by syncthing (but the ownership will be reset to you). Directories owned by someone else where you don’t have write permissions due to being the the same group or something are of course a problem - they will fail, and be eternally retried.

Syncthing never gives up, and never surrenders. :fist:

Jakob, Thanks a lot for the clarification.

I think I had syncthing in a funny state, and with the short rescan interval and files failing to sync, that caused the high cpu usage.

Thanks again.

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Especially syncthing-inotify does this automatically since v0.6.2.


That didn’t seem to happen for me. I have syncthing-inotify 0.6.7-1 (on Arch Linux). What value does it set the rescan interval to?

It is not exposed in the GUI, since the value is adjusted via the API. You can see it when running with -verbosity=4:

[DEBUG] 12:42:30 Delay scan reminder interval for m-und-s set to 3595 seconds
[TRACE] 12:42:30 Informing ST: m-und-s: [.stfolder]
[OK] 12:42:30 Watching ablage: /home/stefan/Sync/Ablage
[DEBUG] 12:42:30 Delay scan reminder interval for papa set to 3595 seconds

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