Storage device having a controller configured to select modes as write modes based on received instructions, storage system, and control method

Abstract

According to one embodiment, a storage device includes a nonvolatile memory and a controller. The controller is configured to select a first mode as a write mode to write data from the host to the nonvolatile memory when the controller receives a first instruction from the host. In the first mode, n-bit data is written into a memory cell in a first area of the nonvolatile memory, n being a positive integer more than or equal to 1. The controller is configured to select another mode different from the first mode as the write mode when the controller receives a second instruction from the host.

What is claimed is: 
     
         1 . A storage device connectable to a host, comprising:
 a nonvolatile memory; and   a controller configured to control the nonvolatile memory, wherein   the controller is configured to select a first mode as a write mode to write data from the host to the nonvolatile memory when receiving a first instruction from the host;   n-bit data is written into a memory cell in a first area of the nonvolatile memory in the first mode;   n is a positive integer more than or equal to 1;   the controller is configured to select a second mode as the write mode when receiving a second instruction from the host,   m-bit data is written into a memory cell of a second area of the nonvolatile memory in the second mode,   m is a positive integer more than n, and   the controller is configured to stop executing a write operation in the first mode when a write data size in the first mode reaches a target size of data written in the first mode, the target size of data written in the first mode being specified by a third instruction from the host.   
     
     
         2 . The storage device of  claim 1 , wherein
 the controller is configured to stop executing a write operation in the first mode when a data write period in the first mode reaches a target period of a data write period in the first mode, the target period of a data write period in the first mode being specified by a fourth instruction from the host.   
     
     
         3 . The storage device of  claim 1 , wherein
 the controller is configured to select the second mode as the write mode after the controller stops executing a write operation in the first mode.   
     
     
         4 . The storage device of  claim 1 , wherein
 the nonvolatile memory includes blocks, each of the blocks being a unit of data erase;   each of the blocks is an active block storing valid data and a free block storing no valid data; and   the controller is configured to execute a free block generation operation to increase a number of the free blocks in the first area when receiving the second instruction.   
     
     
         5 . The storage device of  claim 4 , wherein
 the free block generation operation includes a garbage collection or a compaction.   
     
     
         6 . The storage device of  claim 4 , wherein
 the controller is configured to stop executing the free block generation operation when a size of the free blocks included in the first area reaches a target size of free blocks included in the first area, the target size of free blocks included in the first area being specified by a fifth instruction received from the host after starting the free block generation operation.   
     
     
         7 . The storage device of  claim 4 , wherein
 the controller is configured to stop executing the free block generation operation when an execution time of the free block generation operation reaches a target execution time of the free block generation operation, the target execution time of the free block generation operation being specified by a sixth instruction from the host.   
     
     
         8 . The storage device of  claim 4 , wherein
 the controller is configured to adjust a priority of the free block generation operation such that a degradation degree of write performance does not exceed an acceptable value of a degradation degree of write performance due to the free block generation operation, the acceptable value of a degradation degree of write performance due to the free block generation operation being specified by a seventh instruction from the host.   
     
     
         9 . The storage device of  claim 8 , wherein the write performance includes at least one of a throughput and a latency. 
     
     
         10 . The storage device of  claim 4 , wherein
 the controller is configured to adjust a priority of the free block generation operation such that a size of the free blocks in the first area reaches a target size of free blocks in the first area, the target size of free blocks in the first area being specified by an eighth instruction received from the host after starting the free block generation operation.   
     
     
         11 . The storage device of  claim 4 , wherein
 the controller does not execute a copy operation for copying valid data in an active block to another active block when-a degree of wear of the nonvolatile memory will exceed a target value of a degree of wear of the nonvolatile memory before executing the copy operation, the target value of a degree of wear of the nonvolatile memory being specified by a ninth instruction from the host.   
     
     
         12 . The storage device of  claim 4 , wherein
 the controller does not execute a copy operation for copying valid data in an active block to another active block when-an average of degrees of wear of the nonvolatile memory will exceed a target value of a degree of wear of the nonvolatile memory before executing the copy operation, the target value of a degree of wear of the nonvolatile memory being specified by a ninth instruction from the host.   
     
     
         13 . A storage system comprising:
 a host; and   a storage device connectable to the host, wherein   the host is configured to transmit a first instruction and a second instruction to the storage device;   the storage device includes a nonvolatile memory and a controller configured to control the nonvolatile memory;   the controller is configured to select a first mode as a write mode to write data from the host to the nonvolatile memory when receiving the first instruction from the host;   n-bit data is written into a memory cell in a first area of the nonvolatile memory in the first mode;   n is a positive integer more than or equal to 1;   the controller is configured to select a second mode as the write mode when receiving the second instruction from the host;   n-bit data is written into a memory cell of a second area of the nonvolatile memory in the second mode,   m is a positive integer more than n, and   the controller is configured to stop executing a write operation in the first mode when a write data size in the first mode reaches a target size of data written in the first mode, the target size of data written in the first mode being specified by a third instruction from the host.   
     
     
         14 . A control method for controlling a nonvolatile memory, comprising:
 selecting a first mode as a write mode to write data from a host to the nonvolatile memory when receiving a first instruction from the host,   selecting a second mode as the write mode when receiving a second instruction from the host,   stopping executing a write operation in the first mode when a write data size in the first mode reaches a target size of data written in the first mode, the target size of data written in the first mode being specified by a third instruction from the host, wherein   n-bit data is written into a memory cell in a first area of the nonvolatile memory in the first mode,   n is a positive integer more than or equal to 1,   m-bit data is written into a memory cell of a second area of the nonvolatile memory in the second mode, and   m is a positive integer more than n.   
     
     
         15 . The storage system of  claim 13 , wherein the host is configured to determine a first mode disable time, a first mode enable time, and the target size of data written in the first mode, transmit the second instruction to the storage device when a current time is the first mode disable time, and transmit the third instruction and the first instruction to the storage device when a current time is the first mode enable time. 
     
     
         16 . The storage system of  claim 15 , wherein the host is configured to transmit the first instruction to the storage device after transmitting the third instruction.