2022
https://habr.com/ru/company/first/blog/668520/
2021
https://www.linuxshelltips.com/sync-two-web-servers-automatically-rsync/
????
http://www.unixmen.com/synchronize-files-directories-across-systems-using-rsync/

rsync
  -a, --archive
    archive mode (preserve user, group, mod-time, links, other kind of such stuff...)
  --append
    is dangerous and will result in a corrupt file if the data does not match for some reason.
  -l, --links
    copy symlinks as symlinks
  -P
    same as --partial --progress
  -z, --compress
    compress file data during the transfer
  --compress-level=NUM    explicitly set compression level
  --skip-compress=LIST    skip compressing files with a suffix in LIST
  -v, --verbose               increase verbosity
  --info=FLAGS            fine-grained informational verbosity
  --debug=FLAGS           fine-grained debug verbosity
    FLAGS=help            for the list of flags
  --msgs2stderr           special output handling for debugging

Samples:
rsync -aPvz -e ssh /directory/with/files/ you@host.com:/new/directory/

SO:
http://unix.stackexchange.com/questions/2445/resume-transfer-of-a-single-file-by-rsync
http://superuser.com/questions/579001/rsync-does-it-create-a-temp-file-during-transfer