title: How to check the integrity of data backups
body: <p>I have important data that I am backing up locally. I have a working copy of the data on one local hard drive and then a backup on a external hard drive (and then another copy on a server offsite). </p>
  
  <p>Is there a good way for me to do a regular (e.g. weekly) scan of the data integrity to make sure that nothing has become corrupted on either drive?</p>
  
  <p>1) a disk util scan (eg fsck) will check the drive, but not necessarily the data.
  2) an rsync would tell if the versions are different.
  3) a hash on 'completed' folders?</p>
  
  <p>Any other better ways to check the integrity of the data on disks to make sure that nothing has been corrupted?</p>