Drobo 2. Gen does not mount after restart

Hello community. Whenever I restart my iMac OSX 10.7.5 connected via firewire to my drobo, it is no longer visible on the desktop and the Time Machine Backup cannot start. But it appears in the drobo dashboard and shows having no problem. It takes me a 3 days repair with DiskWarrior to make it visible again. My next restart brings me back to the beginning. What to do to create a stable connection? Please send me your advice. (Updating to an newer Mac OS is not an option for me due to certain software.)