A direct memory access (DMA) engine has virtually all control in
connection with data transfers that can involve one or both of primary
and secondary controllers. The DMA engine receives a command related to a
data transfer from a processor associated with the primary controller.
This command causes the DMA engine to access processor memory to obtain
metadata therefrom. In performing a DMA operation, the metadata enables
the DMA engine to conduct data transfers between local memory and remote
memory. In performing exclusive OR operations, the DMA engine is involved
with conducting data transfers using local memory.