Drobo Pros tend to die and reboot if the iscsi parameters are not right on the initiator (on the client).
As such, we need to make sure the following parameters are set in the iscsi (client) configuration file for the drobo node (change this in /etc/iscsi/iscsid.conf for it to be reboot-persistent):
node.session.cmds_max = 16 node.session.queue_depth = 16 node.conn[0].tcp.window_size = 65535
A more complete article is here: http://www.thirdmartini.com/index.php/DroboPro,_iSCSI_and_Linux