Before updating your Drobo storage device's firmware, please make sure to read the an important article from our knowlege base:

Why can't I upgrade the firmware on my Drobo S, connected via eSATA?

If the size of your volume on the Drobo S is greater than 2TB, you will likely not be able to update the firmware while using the eSATA connection. We are aware of this issue and will release a fix soon.

In the meantime, please do the following:

1. Safely shut down your Drobo S.
2. Disconnect the eSATA cable and use either the FireWire or USB connection.
3. Turn the Drobo S back on and let it finish booting.
4. Update the firmware. In Drobo Dashboard, click Advanced Controls -> Tools -> Check for updates.
5. Drobo Dashboard will walk you through the process.
6. After the unit reboots from the update process, safely shut down your Drobo S again.
7. Disconnect the FireWire or USB cable and connect the eSATA cable.
8. Toggle the power switch on the back of your Drobo S.
9. Check the firmware version to make sure the update was successful: Advanced Controls -> Tools and then check the "Installed Versions" pane at the bottom right of the window.
   

http://support.datarobotics.com/app/answers/detail/a_id/127/