my Drobo has been running for years without problems. The setup is:
4 drives: 750 GB, 2000 GB, 750 GB and 500 GB. Data usage: 20%, 80% free. In the last few weeks I have an interesting phenomenon. When I start the computer - Mac - the first drive has a red light, not blinking - indicating that the drive is close to full. After about 30 sec to 1 min it turns into green and everything is back to normal.