Upon rebooting a server, the addressing often changes. This means the addressing you configured within OSB is no longer valid and needs to be updated. You can configure persistant bindings in os or hba which will keep addresssing the same after reboot. This configuration is outside of OSB. There is a MOS note showing an example of how to configure persistant bindings with at os level.
You should insure that a drive is unloaded (ie no tape in it) before removing it from service.