Storage system and storage system control method

Abstract

A storage system of the present invention improves the response performance of sequential access to data, the data arrangement of which is expected to be sequential. Data to be transmitted via streaming delivery is stored in a storage section. A host sends data read out from the storage section to respective user machines. A prefetch section reads out from the storage section ahead of time the data to be read out by the host, and stores it in a cache memory. A fragmentation detector detects the extent of fragmentation of the data arrangement in accordance with the cache hit rate. The greater the extent of the fragmentation, the smaller the prefetch quantity calculated by a prefetch quantity calculator. A prefetch operation controller halts a prefetch operation when the extent of data arrangement fragmentation is great, and restarts a prefetch operation when the extent of fragmentation decreases.

1 . A storage system comprising: 
 a storage apparatus comprising at least one or more rewritable storage devices for storing data expected to be read out sequentially;    a cache memory for storing the data to be read out from the storage apparatus;    a prefetch section for reading out, in advance, the data stored in the storage apparatus and storing the data in the cache memory before a sequential read access is received from a host;    a continuity determination section for determining the continuity of the arrangement of the data stored in the storage apparatus;    a prefetch quantity calculator for calculating a prefetch quantity on the basis of the result of a determination by the continuity determination section and the state of a read access from the host; and    a prefetch operation controller for setting the prefetch quantity calculated by the prefetch quantity calculator in the prefetch section, and controlling the operation of the prefetch section based on the determination result by the continuity determination section.    
   
   
       2 . The storage system according to  claim 1 , wherein the continuity determination section digitizes and outputs the continuity of the arrangement of the data stored in the storage section based on the read access cache hit rate.  
   
   
       3 . The storage system according to  claim 1 , wherein the prefetch operation controller halts a prefetch operation by the prefetch section when the determination result by the continuity determination section is equal to or less than a prescribed value set beforehand.  
   
   
       4 . The storage system according to  claim 1 , wherein the prefetch operation controller operates a prefetch operation by the prefetch section when the determination result by the continuity determination section is equal to or greater than another prescribed value set beforehand.  
   
   
       5 . The storage system according to  claim 1 , wherein the prefetch operation controller halts a prefetch operation by the prefetch section when the determination result by the continuity determination section is equal to or less than a prescribed value set beforehand, and restarts the prefetch operation when the determination result is equal to or greater than another prescribed value set beforehand.  
   
   
       6 . The storage system according to  claim 3  or  claim 5 , wherein the continuity determination section digitizes and outputs the continuity of the arrangement of the data stored in the storage section based on the read access cache hit rate, and, when the prefetch operation is halted, determines the continuity of the arrangement of the data during the prefetch operation halt period by predicting the cache hit rate for the prefetch operation halt period.  
   
   
       7 . The storage system according to  claim 1 , wherein the prefetch quantity calculator calculates the prefetch quantity on the basis of a maximum data quantity of a readout request from the host within a single cycle of a prefetch operation by the prefetch section.  
   
   
       8 . The storage system according to  claim 1 , wherein the prefetch quantity calculator uses a maximum data quantity of a readout request from the host within a single cycle of a prefetch operation by the prefetch section as a maximum prefetch quantity, and calculates the prefetch quantity by multiplying the digitized determination result in accordance with the continuity determination section by this maximum prefetch quantity.  
   
   
       9 . The storage system according to  claim 1 , wherein the prefetch operation controller outputs an alert when halting a prefetch operation by the prefetch section.  
   
   
       10 . The storage system according to  claim 1 , wherein the prefetch operation controller outputs an alert when halting a prefetch operation by the prefetch section, and starts up a rearrangement process for consecutively arranging the data stored in the storage apparatus.  
   
   
       11 . The storage system according to  claim 1 , wherein the prefetch section, the continuity determination section, the prefetch quantity calculator, and the prefetch operation controller respectively operate for each of logical volumes provided in the storage device.  
   
   
       12 . The storage system according to  claim 1 , wherein the prefetch operation controller comprises a first mode, in which a prefetch operation is performed by setting in the prefetch section the prefetch quantity calculated by the prefetch quantity calculator, and a second mode, in which a prefetch operation is performed in the prefetch section based on a preset initial value.  
   
   
       13 . The storage system according to  claim 12 , wherein the prefetch operation controller operates the prefetch section in the second mode until the prefetch quantity calculator and the continuity determination section become operable, and performs transitions from the second mode to the first mode when the prefetch quantity calculator and the continuity determination section become operable.  
   
   
       14 . A control method for controlling a storage system which sends data to a host in response to a sequential read access from the host, the method executing the steps of: 
 executing a prefetch operation, which reads out, in advance, data stored in a storage apparatus at a predetermined cycle and stores the data in a cache memory, prior to receiving a sequential read access from a host;    determining the continuity of the arrangement of the data stored in the storage apparatus based on the read access cache hit rate from the host;    calculating a prefetch quantity to be utilized in the prefetch operation, on the basis of a determination result by the continuity determination step and a maximum data quantity required by the read access within the predetermined cycle; and    controlling prefetch operation for either operating or halting the prefetch operation on the basis of a determination result by the continuity determination step.    
   
   
       15 . A storage control device respectively connected to a storage apparatus comprising at least one or more rewritable storage devices for storing data expected to be read out sequentially, and a host, which issues a sequential read access to the storage apparatus, the storage control device comprising: 
 a cache memory for storing the data to be read out from the storage apparatus;    a prefetch section for reading out, in advance, the data stored in the storage apparatus and storing the data in the cache memory, prior to receiving a sequential read access from a host;    a continuity determination section for determining the continuity of the arrangement of the data stored in the storage apparatus;    a prefetch quantity calculator for calculating a prefetch quantity based on a determination result by the continuity determination section and the state of a read access from the host; and    a prefetch operation controller for setting the prefetch quantity calculated by the prefetch quantity calculator in the prefetch section, and for controlling the operation of the prefetch section based on a determination result by the continuity determination section.