Semiconductor storage device with volatile and nonvolatile memories to allocate blocks to a memory and release allocated blocks
A semiconductor storage device includes a first memory area configured in a volatile semiconductor memory, second and third memory areas configured in a nonvolatile semiconductor memory, and a controller which executes following processing. The controller executes a first processing for storing a plurality of data by the first unit in the first memory area, a second processing for storing data outputted from the first memory area by a first management unit in the second memory area, and a third processing for storing data outputted from the first memory area by a second management unit in the third memory area.
1. A semiconductor storage device comprising:
an interface configured to receive data from an external host apparatus;
a first memory configured to store the data by a first unit or less, the first unit being an access unit from the external host apparatus;
a nonvolatile memory configured to store the data transmitted from the interface via the first memory; and
a controller configured to:
allocate a plurality of blocks to a first memory area in the nonvolatile memory, each plurality of blocks being a unit of data erasing, the plurality of blocks allocated to the first memory area including SLC (Single Level Cell) blocks;
allocate at least one of the SLC blocks to a second memory area in the nonvolatile memory from the first memory area, a plurality of blocks allocated to the second memory area including SLC blocks and MLC (Multi Level Cell) blocks;
store a plurality of data in the first memory by the first unit;
store data outputted from the first memory in the SLC block in the first memory area by a first management unit, the first management unit being twice or larger natural number times as large as the first unit and being less than the unit of data erasing;
copy valid data stored in the SLC blocks to one of the MLC blocks when a first condition is satisfied; and
release at least one of the SLC blocks in which no valid data is stored from the second memory area, after copying the valid data stored in the SLC blocks.
2. The semiconductor storage device according to claim 1 , wherein the controller is configured to allocate the at least one of the SLC blocks to the second memory area from the first memory area when a number of valid data stored in the at least one of the SLC blocks in the first memory area is a first threshold or more.
3. The semiconductor storage device according to claim 2 , wherein the controller is configured to copy valid data stored in at least one of the SLC blocks in the first memory area to one of the MLC blocks when the number of valid data stored in the at least one of the SLC blocks in the first memory area is less than the first threshold.
4. The semiconductor storage device according to claim 1 , wherein
the first condition is satisfied when a number of the SLC and MLC blocks allocated to the second memory area exceeds a second threshold, and
the controller copies valid data stored in the SLC blocks to one of the MLC blocks, within the second memory area, when the first condition is satisfied.
5. The semiconductor storage device according to claim 1 , wherein the SLC blocks include pseudo SLC blocks.
6. The semiconductor storage device according to claim 1 , wherein a programming time for an SLC block is shorter than that for an MLC block.
7. The semiconductor storage device according to claim 1 , wherein a capacity of an SLC block is smaller than that of an MLC block.
8. The semiconductor storage device according to claim 7 , wherein the controller is configured to invalidate first data, the first data having the same logical address as data newly stored to the first memory area, stored in the first or second memory area.
9. The semiconductor storage device according to claim 8 , wherein the controller is configured to manage the SLC blocks allocated to the first memory area with FIFO (First In First Out) data structure sorted by an allocation order.
10. The semiconductor storage device according to claim 9 , wherein the controller is configured to, when storing data to the first memory area, allocate a new SLC block to the first memory area at an input side of the FIFO data structure.
11. The semiconductor storage device according to claim 10 , wherein the controller is configured to allocate an SLC block having an oldest allocation order at an output side of the FIFO data structure to the second memory area.
12. The semiconductor storage device according to claim 1 , wherein a number of blocks allocatable to the first memory area has an upper limit.
13. The semiconductor storage device according to claim 12 , wherein the controller is configured to allocate at least one of the SLC blocks to the second memory area when a number of the SLC blocks allocated to the first memory area exceeds the upper limit.
14. The semiconductor storage device according to claim 1 , wherein the nonvolatile memory is a NAND type flash memory.
15. The semiconductor storage device according to claim 1 , wherein the nonvolatile memory includes a plurality of memory chips.
16. The semiconductor storage device according to claim 1 , wherein the first memory is a DRAM (Dynamic Random Access Memory).
17. A method of controlling a semiconductor storage device, the semiconductor storage device including a nonvolatile memory and a first memory, the method comprising:
receiving data from an external host apparatus;
storing the data by a first unit or less in the first memory, the first unit being an access unit from the external host apparatus;
allocating a plurality of blocks to a first memory area in the nonvolatile memory, each plurality of blocks being a unit of data erasing, the plurality of blocks allocated to the first memory area including SLC (Single Level Cell) blocks;
allocating at least one of the SLC blocks to a second memory area in the nonvolatile memory from the first memory area, a plurality of blocks allocated to the second memory area including SLC blocks and MLC (Multi Level Cell) blocks;
storing the data in the SLC block in the first memory area by a first management unit, the data being stored in the first memory, the first management unit being twice or larger natural number times as large as the first unit and being less than the unit of data erasing;
copying valid data stored in the SLC blocks to one of the MLC blocks when a first condition is satisfied; and
releasing at least one of the SLC blocks in which no valid data is stored from the second memory area, after copying the valid data stored in the SLC blocks.
18. The method according to claim 17 , wherein the allocating the at least one of the SLC blocks to the second memory area is executed when a number of valid data stored in the at least one of the SLC blocks in the first memory area is a first threshold or more.
19. The method according to claim 18 , wherein the copying is executed when the number of valid data stored in the at least one of the SLC blocks in the first memory area is less than the first threshold.
20. The method according to claim 17 , wherein
the first condition is satisfied when a number of the SLC and MLC blocks allocated to the second memory area exceeds a second threshold, and
the copying includes copying valid data stored in the SLC blocks to one of the MLC blocks, within the second memory area, when the first condition is satisfied.