IBM DS4000 Auto Volume Transfer Usage With RDAC

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The IBM System Storage DS4000 Series are IBM's solution for mid-range or departmental storage requirements. In a DS4000 storage subsystem equipped with two controllers, one can provide redundant I/O paths between the host systems and the storage. There are two different components that provide redundancy in the I/O data paths: the Auto Volume Transfer (AVT) feature of the storage subsystem and a host multi-path driver, for example, Redundant Disk Array Controller (RDAC). This paper is to provide an overview of AVT and RDAC, and introduce how AVT works with RDAC depending on the configuration. It also intends to illustrate several possible path thrashing situations with the AVT mode or not.