restarting jujud will trigger deletion operation, the path of '/var/lib/juju' was removed.

Hi, all:
      I am facing a problem about high available. I try many times for disaster failure drill. I found that the path of '/var/lib/juju/*' was been removed by restarting jujud when my mongodb is empty. what's wrong? How can i do to prevent it removed?
      if anyone can help me, please reply me. Thanks!