Read-write control of data storage disk units

Abstract

The control unit arbitrarily with respect to the CPU, including according to an algorithm that is independent of the request a disk unit among the disk units that are inactive when the control unit receives an input/output request involving either read or staging. For a write request from the CPU, the control unit selects a specific disk unit in the disk unit group for the immediate writing of data. In the second kind of load distribution a disk unit is selected to execute read and staging other than the above-mentioned specific disk.

1 - 24 . (canceled)  
     
     
         25 . A storage system comprising: 
 a first storage unit;    a second storage unit storing identical data of the first storage unit; and    a controller connected to the first storage unit and the second storage unit,    wherein, if the controller receives a read request from a host, the controller executes a first operation reading first data requested by the read request from the first storage unit and executes a second operation prefetching second data corresponding to the first data read by the first operation from the second storage unit.    
     
     
         26 . A storage system according to  claim 25 , 
 wherein a first data transfer operation corresponding to the first operation and a second data transfer operation corresponding to the second operation are executed in parallel.    
     
     
         27 . A storage system according to  claim 26 , 
 wherein the controller includes a memory, and    wherein the controller stores the second data in the memory before executing the second data transfer operation.    
     
     
         28 . A storage system according to  claim 27 , further comprising a third storage unit storing identical data stored in the first storage unit, 
 wherein the controller executes the second operation by using the third storage unit if the second storage is used by another operation.