Not sure of variant to use when simply updating changed files from source

[BARTONLEWIS]

I did my first back up using Mirror variant to create an identical backup of my files. Going forward, I want to continue to make an identical backup by replacing any changed/edited files from the Source in the Backup, and adding new files from the Source to the Backup and deleting files from the Backup that were deleted from the Source. I watched the Tutorials on Mirror and Two Way and it wasn't evident to me that Mirror would update edited files in the Backup. It is also the case that Two Way would perform changes to the Source based on what's in the Backup, which I don't want. The crux of my question I guess is does Mirror look at the date a file was last edited and/or its content and back it up if it's changed from the last sync, or not? If not, what's the best way to achieve my objectives? I'm sorry if I'm missing something obvious. Thanks.

[xCSxXenon]

Use mirror

[Plerry]

> It is also the case that Two Way would perform changes to the Source based on what's in the Backup, which I don't want.

Then you should not use the Two-way variant

> ... and deleting files from the Backup that were deleted from the Source.

That's the difference between the Mirror variant and the Update variant:
The Update variant retains right-side files that do not (or no longer) exist on the left side; the Mirror variant deletes such right-side files.
So, as xCSxXenon wrote, a Mirror sync is your way to go.

[BARTONLEWIS]

OK, thanks. My remaining question is, how does freefilesync know if a file has been edited since the last sync? Does it look at the date of the edit? Presumably, it does not analyze the content of the file. If so, how would it know, for example, that a Photoshop file was changed? I doubt that it is able to determine edits in such a file, and assume it's looking at the date last edited. If that correct? Or would it not update such a file (.PSB, .PSD) if changes were made? Thanks.

[Plerry]

> how does freefilesync know if a file has been edited since the last sync?

If you checkmark "Use database file to detect changes", that database contains the file-IDs of your left-side, respectively right-side files as per the end of a sync. If a file is modified, its file-ID is changed by the OS. So, if the present file-ID of a given file differs from its file-ID at the end of the previous sync (as stored in the database) FFS knows the file is modified and needs to be synced based on the selected sync settings.

If you do not checkmark "Use database file to detect changes", depending on your settings for Compare, FFS compares the left-side file time and size, file content or file size of all files with those at the right-side.
For those files of which that file info differs, FFS determines the required sync actions based on the selected sync settings.

[BARTONLEWIS]

That's super helpful, thanks. It's interesting that that information is not included in the Tutorial, but, regardless, it sounds like either way an updated (edited) file will be detected.

[Zenju]

If you checkmark "Use database file to detect changes", that database contains the file-IDs of your left-side, respectively right-side files as per the end of a sync. If a file is modified, its file-ID is changed by the OS. So, if the present file-ID of a given file differs from its file-ID at the end of the previous sync (as stored in the database) FFS knows the file is modified and needs to be synced based on the selected sync settings.

No, FFS uses time and date in order to detect a changed file. The file ID is used for detection of moved files.

[Plerry]

@Zenju
Thanks for the correction.