[Borgbackup] (too) many modified files

[Thomas Waldmann]

> looking for possible reasons for long backup duration, I added these 
> options to the borg command line:
> -v --list --filter=AMCE --stats --show-rc -C zstd
> and pipe it to al log file. Therin, I found 524 files marked "A" solely 
> from my own home directory. As far as I understand this means that 524 
> files are new and added to the repo within one day. That sounds plausible.
> 
> But I found more than 600k files marked "M".

https://borgbackup.readthedocs.io/en/stable/faq.html#why-is-backup-slow-for-me

"Also, the --debug-topic=files_cache option of borg create provides a 
lot of debug output helping to analyse why the files cache does not give 
its expected high performance."

So, did you already use that?

> Does that mean that these 
> files are identified as modified and added to the repo as well?

Yes, M means modified.

> If so, this must be an error, since (almost?) all of them weren't 
> touched for years.

Run it with that option and it will log why it considers them modified.

Could be:
- content modified (and you are not aware)
- metadata modified (some chown/chmod -R maybe? or xattrs changes?)
- inode numbers not stable (you can switch that off in borg, if you need to)