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 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;   a first queue corresponds to the first storage unit;   a second queue corresponds to the second storage unit; and   a 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.   
     
     
         2 . The data storage device of  claim 1 , wherein
 the distributor distributes a write command having a smaller data length to the second queue preferentially than a write command having a larger data length.   
     
     
         3 . The data storage device of  claim 1 , wherein
 upon being notified from the host that an expectation value of an access to data designated by the write command is high, the distributor distributes the write command to the second queue preferentially.   
     
     
         4 . A data storage device comprising:
 a first storage unit;   a second storage unit 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; and   a controller measures the number of accesses in response to a read command from the host, to data not stored in the second storage unit but stored in the first storage unit and writes the data stored in the first storage unit to the second storage unit based on the measured number of accesses.   
     
     
         5 . The data storage device of  claim 4 , wherein
 the controller writes the data stored in the first storage unit to the second storage unit when the number of accesses is 2 or more.   
     
     
         6 . The data storage device of  claim 4 , wherein
 upon receiving the read command from the host, the controller writes the data stored in the first storage unit to the second storage unit and sends the data to the host when the length of the data designated by the read command is a predetermined value or smaller, and sends the data stored in the first storage unit to the host without writing the data to the second storage unit when the length of the data designated by the read command exceeds the predetermined value.   
     
     
         7 . The data storage device of  claim 4 , wherein
 the controller writes the data stored in the first storage unit to the second storage unit when no access has been made from the host for a predetermined period or more and the number of accesses is a predetermined value or more.   
     
     
         8 . The data storage device of  claim 4 , wherein
 the controller resets the number of accesses according to a write command from the host.   
     
     
         9 . A data storage control method in a data storage device which includes a first storage unit, a second storage unit 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, a first queue corresponds to the first storage unit, and a second queue corresponds to the second storage unit, the method comprising:
 distributing 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.   
     
     
         10 . The data storage control method of  claim 9 , wherein
 a write command having a smaller data length is distributed to the second queue preferentially than a write command having a larger data length.   
     
     
         11 . The data storage control method of  claim 9 , wherein
 when it is notified from the host that an expectation value of an access to data designated by the write command is high, the write command is distributed to the second queue preferentially.   
     
     
         12 . A data storage control method in a data storage device which includes a first storage unit, and a second storage unit 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 method comprising:
 measuring the number of accesses in response to a read command from the host, to data not stored in the second storage unit but stored in the first storage unit and writing the data stored in the first storage unit to the second storage unit based on the measured number of accesses.   
     
     
         13 . The data storage control method of  claim 12 , wherein
 the data stored in the first storage unit is written to the second storage unit when the number of accesses is 2 or more.   
     
     
         14 . The data storage control method of  claim 12 , wherein
 upon receiving the read command from the host, the data stored in the first storage unit is written to the second storage unit and the data is sent to the host when the length of the data designated by the read command is a predetermined value or smaller, and the data stored in the first storage unit is sent to the host without writing the data to the second storage unit when the length of the data designated by the read command exceeds the predetermined value.   
     
     
         15 . The data storage control method of  claim 12 , wherein
 the data stored in the first storage unit is written to the second storage unit when no access has been made from the host for a predetermined period or more and the number of accesses is a predetermined value or more.   
     
     
         16 . The data storage control method of  claim 12 , wherein
 the number of accesses is reset according to a write command from the host.