MEMORY DEVICE THAT PERFORMS GARBAGE COLLECTION
A memory device includes a nonvolatile memory unit including a plurality of blocks, and a memory controller. The memory controller is configured to determine target blocks for garbage collection, and transfer valid data in the target blocks to another block during the garbage collection. The target blocks includes a first block that has a valid data ratio greater than zero and equal to or smaller than a predetermined value and a second block that has a valid data ratio greater than the predetermined value.
1 . A memory device, comprising:
a nonvolatile memory unit including a plurality of blocks; and
a memory controller configured to determine target blocks for garbage collection, the target blocks including a first block that has a valid data ratio greater than zero and equal to or smaller than a predetermined value and a second block that has a valid data ratio greater than the predetermined value, and transfer valid data in the target blocks to another block during the garbage collection.
2 . The memory device according to claim 1 , wherein
a block that has the smallest valid data ratio of a plurality of blocks that have a valid data ratio greater than zero and equal to or smaller than the predetermined value is determined to be the first block.
3 . The memory device according to claim 1 , wherein
a block that has the largest valid data ratio of a plurality of blocks that have a valid data ratio greater than the predetermined value is determined to be the second block.
4 . The memory device according to claim 1 , wherein
the memory controller is further configured to maintain a first list containing one or more blocks having a valid data ratio that is greater than zero and equal to or smaller than the predetermined value, and a second list containing one or more blocks having a valid data ratio that is greater than the predetermined value, and
one of the blocks in the first list is determined to be the first block, and one of the blocks in the second list is determined to be the second block.
5 . The memory device according to claim 4 , wherein
the memory controller is further configured to
determine whether or not a data size of the valid data in the first block is equal to or greater than a predetermined size, and
when the data size is smaller than the predetermined size, determine one or more other blocks in the first list to be the target blocks for the garbage collection.
6 . The memory device according to claim 5 , wherein
the memory controller is further configured to determine the number of blocks in the first list, that are determined to be the target blocks, and
when the number is greater than a predetermine number, the memory controller determines no other block in the first list to be the target block for the garbage collection.
7 . The memory device according to claim 4 , wherein
the second list contains one or more blocks that have a valid data ratio greater than the predetermined value and indicates an elapsed time, which is a time that has passed since oldest valid data was written therein, greater than a predetermined value.
8 . The memory device according to claim 7 , wherein
a block in the second list, that has the largest elapsed time is determined to be the second block.
9 . The memory device according to claim 4 , wherein
a block in the second list, that has been subjected to erasing the least number of times is determined to be the second block.
10 . The memory device according to claim 1 , wherein
the nonvolatile memory unit includes a NAND-type flash memory.
11 . A method for managing data stored in a nonvolatile memory unit that includes a plurality of blocks, the method comprising:
determining target blocks for garbage collection, including a first block that has a valid data ratio greater than zero and equal to or smaller than a predetermined value and a second block that has a valid data ratio greater than the predetermined value; and
transferring valid data in the target blocks to another block.
12 . The method according to claim 11 , wherein
a block that has the smallest valid data ratio of a plurality of blocks that have a valid data ratio greater than zero and equal to or smaller than the predetermined value is determined to be the first block.
13 . The method according to claim 11 , wherein
a block that has the largest valid data ratio of a plurality of blocks that have a valid data ratio greater than the predetermined value is determined to be the second block.
14 . The method according to claim 11 , further comprising:
maintaining a first list containing one or more blocks having a valid data ratio that is greater than zero and equal to or smaller than the predetermined value and a second list containing one or more blocks having a valid data ratio that is greater than the predetermined value, wherein
one of the blocks in the first list is determined to be the first block, and one of the blocks in the second list is determined to be the second block.
15 . The method according to claim 14 , further comprising:
determining whether or not a data size of the valid data in the first block is equal to or greater than a predetermined size; and
when the data size is smaller than the predetermined size, determining one or more other blocks in the first list to be the target blocks for the garbage collection.
16 . The method according to claim 15 , further comprising:
determining the number of blocks in the first list, that are determined to be the target blocks; and
when the number is greater than a predetermine number, no other block in the first list is determined to be the target block for the garbage collection.
17 . The method according to claim 14 , wherein
the second list contains one or more blocks that have a valid data ratio greater than the predetermined value and indicates an elapsed time, which is a time that has passed since oldest valid data was written therein, greater than a predetermined value.
18 . The method according to claim 17 , wherein
a block in the second list, that has the largest elapsed time is determined to be the second block.
19 . The method according to claim 14 , wherein
a block in the second list, that has been subjected to erasing the least number of times is determined to be the second block.
20 . The method according to claim 11 , wherein
the nonvolatile memory unit includes a NAND-type flash memory.