title: Compare two directory trees
body: <p>I have a btrfs-filesystem consisting of several harddrives in which is stored about 11 TB of Data. My backup consists of a NAS which exports one path via NFS. The path is then mounted on the machine with the btrfs-bilesystem and rsync is called to keep the nfs export synced to the main filesystem. I call rsync with one  -v and send the results of the run to my email account to be sure everything is synchronized correctly. Now by pure chance I found out that some directories were not synchronized correctly - the directories existed on the NAS but they were empty. It is most likely not a rights issue since rsync is run as root. So it seems that in my situation rsync is not entirely trustworthy but I would like to compare the two directory trees to see if there are any files missing on the NAS and/or if there are files which dont exists on the btrfs anymore and which should have been deleted by rsync according. (I use the --delete option). </p>
  
  <p>I am therefore looking for for a program or a script which can help me to check is rsync is running correctly. I don't need anything complicated like checksums, all I want to know if the NAS contains all the files in the btrfs-filesystem.</p>
  
  <p>Any suggestions where to start looking?</p>
  
  <p>Yours, Stefan</p>