[Borgbackup] Can't figure out why files are being detected as modified (files created by backintime)

[Thomas Waldmann]

> I have a folder created with backups created by backintime. I am now 
> trying to back this up to another disk. Every time I run the backup borg 
> detects all files as modified and reads them. The deduplication avoids 
> writing new data but it still reads 500GB every time I run borg.
> 
> I have set  "-files-cache mtime,size" bit it still detects all files as 
> changed. Are there any other properties that make borg think a file may 
> have been changed?

Did you check the FAQ about this?

In your case (--files-cache=mtime,size), only this is relevant:
- mtime
- size
- full absolute path of the file

Also, when changing --files-cache type, you always need to do >= 2 
backups to see whether it works.

If you have a lot of different backup sets, BORG_FILES_CACHE_TTL might 
be relevant (if the default is too low for your use case).

If you use BORG_FILES_CACHE_SUFFIX badly, that could also make it 
malfunction.

 From borg 1.1.16 changelog entry:

verbose files cache logging via –debug-topic=files_cache, #5659.

Use this if you suspect that borg does not detect unmodified files as 
expected.

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