A sod roll picker including a pair of right facing spear bar assemblies and a pair of left facing spear bar assemblies. When a preceding vehicle exists in the state that the automatic follow-up control is canceled and a state that the intervehicle time is set to a value within a set range continues for a set period of time, it is determined that the own vehicle is in a follow-up driving state executed by the driver. Storage virtualization systems migrate, redirect or synchronize data between a primary and a secondary NAS. If there is a breakdown, the method will enable determination of the location of the breakdown in the gate oxide.