Storage system which utilizes two kinds of memory devices as its cache memory and method of controlling the storage system

Abstract

Provide is a storage system including one or more disk drives, and one or more cache memories for temporarily storing data read from the disk drives or data to be written to the disk drives, in which: the cache memories includes volatile first memories and non-volatile second memories; and the storage system receives a data write request, stores the requested data in the volatile first memories, selects one of memory areas of the volatile first memories if a total capacity of free memory areas contained in the volatile first memories is less than a predetermined threshold, write data stored in the selected memory area in the non-volatile second memories, and changes the selected memory area to a free memory area. Accordingly, there can be realized capacity enlarging of the cache memory using a non-volatile memory device while realizing a high speed similar to that of a volatile memory device.

1 . A storage system comprising:
 a plurality of drives storing data and configuring a plurality of RAID groups; and   a cache memory controller coupled to a random access memory, and a flash memory whose capacity is larger than capacity of the random access memory,   wherein the cache memory controller temporarily stores data read from the plurality of drives to the random access memory, and transfers data stored In the random access memory to the flash memory,   wherein if a first data corresponding to a read request is stored in the random access memory, the cache memory controller reads the first data from the random access memory, and   wherein if the first data is not stored in the random access memory and stored in the flash memory, the cache memory controller reads the first data from the flash memory.   
     
     
         2 . A storage system according to  claim 1 , wherein the data transferred from the random access memory to the flash memory is clean data. 
     
     
         3 . A storage system according to  claim 1 , wherein the cache memory controller selects clean data from data stored in the random access memory, and transfers the clean data from the random access memory to the flash memory, thereby storing the clean data in the flash memory. 
     
     
         4 . A storage system according to  claim 1 , further comprising:
 a first interface coupled to a host computer; and   a second interface coupled to the plurality of drives,   wherein if the first data is not stored in both the random access memory and the flash memory, the second interface reads the first data from the plurality of drives and transfers the first data to the cache memory controller to store the first data in the random access memory.   
     
     
         5 . A storage system according to  claim 4 , wherein the cache memory controller transfers certain clean data from the random access memory to the flash memory if the random access memory does not have a free area for storing the first data transferred from the plurality of drives. 
     
     
         6 . A storage system according to  claim 4 , wherein the cache memory controller transfers certain clean data from the random access memory to the flash memory if an amount of free areas in the random access memory is smaller than a threshold. 
     
     
         7 . A storage system according to  claim 1 , wherein performance of the flash memory is lower than performance of the random access memory. 
     
     
         8 . A storage system according to  claim 1 , wherein data transferred from the random access memory to the flash memory is the least recently used data. 
     
     
         9 . A storage system comprising:
 a plurality of drives storing data and configuring a plurality of RAID groups;   a random access memory temporarily storing data transferred from the plurality of drives; and   a flash memory temporarily storing data transferred from the random access memory,   wherein the capacity of the flash memory is larger than that of the random access memory; and   a cache memory controller coupled to the random access memory and the flash memory,   wherein after the storage system receives a read request, the cache memory controller reads a first data corresponding to the read request from the random access memory if the first data is stored in the random access memory, and reads the first data from the flash memory if the first data is not stored in the random access memory and stored in the flash memory.   
     
     
         10 . A storage system according to  claim 9 , wherein the data transferred from the random access memory to the flash memory is clean data. 
     
     
         11 . A storage system according to  claim 9 , wherein the cache memory controller selects clean data from data stored in the random access memory, and transfers the clean data from the random access memory to the flash memory to store the clean data in the flash memory. 
     
     
         12 . A storage system according to  claim 9 , further comprising:
 a first interface coupled to a host computer; and   a second interface coupled to the plurality of drives,   wherein after the first interface receives the read request, and if the first data is not stored in both the random access memory and the flash memory, the second interface reads the first data from the plurality of drives and transfers the first data to the cache memory controller to store the first data in the random access memory.   
     
     
         13 . A storage system according to  claim 12 , wherein the cache memory controller transfers certain clean data from the random access memory to the flash memory if the random access memory does not have free area for storing the first data transferred from the plurality of drives. 
     
     
         14 . A storage system according to  claim 12 , wherein the cache memory controller transfers certain clean data from the random access memory to the flash memory if an amount of free areas in the random access memory is smaller than a threshold. 
     
     
         15 . A storage system according to  claim 9 , wherein performance of the flash memory is lower than performance of the random access memory. 
     
     
         16 . A storage system according to  claim 9 , wherein data transferred from the random access memory to the flash memory is the least recently used data.