Raid apparatus storing a plurality of same logical volumes on different disk units

Abstract

Disclosed is a RAID apparatus having a plurality of same logical volumes allocated on a real volume. The real volume is so designed that a plurality of same logical volumes are respectively allocated on different physical disk units and a combination of a plurality of logical volumes allocated on each physical disk unit differs from one physical disk unit to another. This structure prevents uneven loading on the real volume from occurring due to uneven loads on the logical volumes.

What is claimed is:  
     
         1 . A RAID apparatus comprising: 
 a real volume including a plurality of physical disk units on each of which a plurality of logical volumes are allocated, and a disk controller for accessing any physical disk unit where a designated logical volume is allocated in order to access said designated logical volume,    said real volume being designed in such a manner that a plurality of same logical volumes are respectively allocated on different physical disk units and a combination of a plurality of logical volumes allocated on each physical disk unit differs from one physical disk unit to another.    
     
     
         2 . The RAID apparatus according to  claim 1 , wherein said disk controller has a conversion table, for each of said logical volumes, for indicating a plurality of physical disk units where said logical volumes are allocated; and 
 said disk controller selects that physical disk unit where said designated logical volume is allocated by referring to said conversion table.    
     
     
         3 . The RAID apparatus according to  claim 2 , wherein said disk controller has a use table, for each of said physical disk units, for storing information indicative of that physical disk unit being in use; and 
 said disk controller selects an unused one of a plurality of physical disk units where said designated logical volume is allocated, by referring to said use table.    
     
     
         4 . The RAID apparatus according to  claim 2 , wherein said conversion table holds invalid information indicating said associated physical disk unit is invalid; and 
 said disk controller selects a valid physical disk unit by referring to said invalid information.    
     
     
         5 . The RAID apparatus according to  claim 4 , wherein said conversion table holds invalid information for an invalid physical disk unit as information indicating said invalid physical disk unit.  
     
     
         6 . The RAID apparatus according to  claim 1 , wherein said plurality of same logical volumes are allocated at same storage positions in said physical disk units.  
     
     
         7 . The RAID apparatus according to  claim 1 , wherein the number of same logical volumes allocated on said real volume differs among said logical volumes.  
     
     
         8 . The RAID apparatus according to  claim 7 , wherein said disk controller has a conversion table, for each of said logical volumes, for holding information indicating a plurality of physical disk units where said logical volumes are allocated, and information indicating the number of said allocated same logical volumes; and 
 said disk controller selects that physical disk unit where said designated logical volume is allocated by referring to said conversion table.