Issue: Upload and Download speeds stuck at 0 B/s

Any thoughts?

Hey, this started happening again, but I did some digging around and I believe it has to do with the way ST Folders on NAS devices are scanned. If I have 2+ (rather large) ST Folders on a NAS being scanned at a time, even if I have other folders which are smaller and local that need to be synced, the “scan” process holds everything else up. If I “pause” one of the (rather large) NAS ST Folders, the other processes begin to resume and I’ll see some (little, but still measurable) synchronization happen to the rest of my Syncthing. If I “pause” both NAS ST Folders holding everything up, ST continues as normal. If and/or when I “continue” or ‘unpause’ my NAS-connected ST Folders, SyncThing again begins to slow down to a screeching halt.

I am thinking of a few different fixes that can be implemented into the app:

  • Have ST save indexing data for NAS shares on the local disk, referencing that if and when the NAS may be too slow to grab a new full index.
  • Limit what types of NAS devices users can sync with in SyncThing, excluding devices that do not reach a certain read-write speed or benchmark.
  • “Scan” should only look for changes, rather than re-scanning the entire directory choice.
  • Etc. (any other ideas?)

What do you mean by “scan”. Syncthing must traverse and “stat” (get metadata of) the entire folder. That’s how it detects changed files. Those and only those files are then rehashed, which is the cpu intensive task. Depending on your hatdware/filesystem, this necessary traverse may already take some time and if this time is bigger than your rescan interval, that’s naturally not ideal and you should adjust that.

During that Syncthing should still send data and eventually also receive some, but if your disk is overloaded by scanning, that may seem like it stalled completely.

There is a feature currently in “testing phase” that can help reduce the need for scans: Continuous change watching, that uses events from the filesystem to detect changed files.

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