A sprinkler and side-loading nozzle insert assembly includes a sprinkler body provided with a flow passage and a nozzle insert seated in a complementary recess in said sprinkler body. A system includes a landline communications network, and a multiline hunt group coupled to the landline communications network. In the route-changing phase, each host computer can access both the old and new storage subsystems and the new storage subsystem writes data into the old storage subsystem in response to a write request from the host computer and reads data from the old storage subsystem and sends the data to the host computer in response to a read request from the host computer.