I am not sure whether I am running into a Syncthing limitation here or just not using it properly. I have what seems like a very simple use case: a folder tree on a Windows PC that needs to be automatically mirrored (one way only) to an Android phone (Samsung Note 4, with Marshmallow 6.1). No files are ever modified on the phone – basically, I’m only using it for backup and reference when I am not near the PC.
So far, I have tried to implement this in two ways. In the beginning, I had set up a bi-directional sync between the PC and phone, and it worked MOST of the time, but then, every once in a while, I would get a massive transfer of files from the phone to the PC with incorrect modification dates, which I clearly had not touched at all at either end (those modification dates were from the very first sync that was done when I originally set up the folder for mirroring). It was as though Syncthing would periodically lose track of some of the files in its index and started seeing them as “modified,” based on the original sync date. I would not lose the data in those files per se, as their contents were unchanged, but this spurious syncing would massively screw up the modification dates throughout my PC folder tree. Most of the times, it was just a few files, or a single subfolder, other times it was much more substantial. I could never find any rhyme or reason as to why certain files suffered this fate at certain times and others did not.
After a couple of major debacles with that first setup, where I ended up having to restore gigabytes of documents from another backup, I clearly could no longer tolerate such risks, so I changed the PC-side folder to “Send only”. This protected it from being overwritten by the spurious syncing events, but now, I regularly get “Out of sync” notifications on the PC, which I have to resolve by manually clicking on the red button to override the warning and force the sync to go ahead.
I see two issues at play here: 1) fundamentally, there is a problem with Syncthing sporadically detecting the original sync dates on the Android device as modifications; 2) there is no configuration option to bypass the “Out of sync” warning on send-only devices, so that the sync can procede without a manual override. I realize that the latter would be just a workaround, but it would still be extremely useful to me under the circumstances, as it would free me from having to constantly go in and override the warning. Mirroring is a common need, so I think an automatic override would be beneficial to many people.
Of course, the root issue of the index losing track of some files and misinterpreting the mdates is the one that really needs to be diagnosed and solved, but for now I would be content with just having an automatic “Out of sync” override option. Or am I missing something here that will allow me solve this problem in some other way?