title: Clone a folder / raid on a folder?
body: <p>I have two hard drive of 4Tb connected to my raspberry pi.
  Let's call them A and B.</p>
  
  <p>I have some folders on A that have to be copied on B. At all the time, something like a RAID10 on some folder. So, if I copy test.jpg in disk A, test.jpg has to be copied on disk B. If I copy test2.jpg on B, test2.jpg has to be copied on A.</p>
  
  <p>So in case A or B crash, I still have an valid, up to date, copy of my files.</p>
  
  <p>Is there anything that exist already ? Or should I use rsync and use it through service ?</p>