Data storage device and data storage control method

Abstract

According to one embodiment, a data storage device includes a first storage unit, a second storage unit, a first queue, a second queue, and a distributor. The second storage unit is used as a cache of the first storage unit and has a lower write transfer rate and a faster response time than the first storage unit. The first queue corresponds to the first storage unit. The second queue corresponds to the second storage unit. The distributor distributes a write command received presently from a host to one of the first and second queues in which the number of write commands registered presently is smaller.

What is claimed is: 
     
         1 . A data storage device comprising:
 a first storage unit;   a second storage unit that has a lower write transfer rate and a faster response time than the first storage unit; and   a controller configured to:   measure a number of accesses, in response to a read command from a host, to first data stored in the first storage unit, and   control to write the first data stored in the first storage unit to the second storage unit in a case where the measured number of accesses is a certain number or more, wherein   the controller controls to write second data to the first storage unit in a case where a write command to overwrite the first data with the second data is received from the host.   
     
     
         2 . The data storage device according to  claim 1 , wherein
 in a case where the read command is received from the host when the first data is stored in the second storage unit, the controller sends the first data from the second storage unit to the host.   
     
     
         3 . The data storage device according to  claim 1 , wherein
 the read command and the write command include a same logical address, and   the controller records the number of accesses in association with the logical address, and resets the number of accesses according to the write command.   
     
     
         4 . The data storage device according to  claim 1 , wherein
 after writing the second data to the first storage unit, the controller measures a number of accesses to the second data stored in the first storage unit, and controls to write the second data stored in the first storage unit to the second storage unit in a case where the measured number of accesses to the second data is the certain number or more.   
     
     
         5 . The data storage device according to  claim 1 , wherein the controller writes the first data stored in the first storage unit to the second storage unit in a case where no access has been made from the host for a certain period or more. 
     
     
         6 . The data storage device according to  claim 1 , wherein
 in a case where the read command from the host, the controller writes the first data stored in the first storage unit to the second storage unit and sends the first data to the host when the length of the first data is a predetermined value or smaller, and sends the first data stored in the first storage unit to the host without writing the first data to the second storage unit when the length of the first data exceeds the predetermined value.