I found from this posting on Stackoverflow, if you just wanted to get a list of corresponding files whose content differs, then you could execute:
diff --brief --recursive dir1/ dir2/
...and trying this myself, this gives a nice little list of files whose content is different.
But if I have made a backup of an original filesystem (assume BIG filesystems, 2TB for example), and I wanted to check if the backup is the same as the original (eg. I want to check if the backup is successful), what should I run, if I am only interested in which files are NOT available on either side? I want something that checks directory trees FAST (not checking contents).
Although comparing the filesize does not give an absolute indication on whether the backed-up file is different, comparing that and other non-filecontent metadata during the comparison command would help.
(My apologies for reposting a very similar question, but I noticed a user arguing that the question was perhaps off-topic, so would this question definitely be on stackoverflow.)
Any experience about this?