[CentOS] [rsync -avz] total size/disk usage difference between source and destination

Thanks for feedback.

After doing a little bit research I found that the application (Apache
Tomcat) and backup (Veritas NetBackup) was running during the copy
job.

What influence have a running Tomcat and NetBackup on rsync?
What rsync (running as root) do if there are read-only files?

kind regards
Sven