[rdiff-backup-users] How does rdiff-backup really detect changed files?

[David Croll]

Dear wizards of rdiff-backup,


as a user of rdiff-backup and main author of the German Wikipedia page 
on rdiff-backup I want to ask you a few questions because the manual 
pages are not very clear on this:

- Is SHA-1 always used to determine if a file has been modified? I 
assume this since the file "mirror_metadata.*.diff.gz" contains the 
SHA-1 digests of the files that have changed since last backup.
- What is the exact meaning of the --verify, --compare-hash and 
compare-full options? They all seem to deal with SHA-1 digests or making 
sure that changed files are indeed copied to the backup directory. This 
is a bit irritating - users might chose the --compare-hash option, but 
rdiff-backup --compare hash <source> <destination> does not actually do 
a backup.

With the very best thanks for this great but yet extremely simple backup 
tool!


David