Storage control apparatus and storage medium

1. A storage control apparatus comprising:

a memory; and

a processor coupled to the memory and configured to:

receive a release request for a first storage area in a virtual storage area,

in response to the receiving of the release request for the first storage area, release, among unit storage areas included in a physical storage area, one or more first unit storage areas allocated to the first storage area from the first storage area to manage each of the released one or more first unit storage areas as an unallocated unit storage area,

execute overwrite processing of writing 0 to each of the released one or more first unit storage areas at a timing asynchronous with a response to the release request for the first storage area, and

in response to a write request to store write data to the virtual storage area, execute write processing including:

allocating the unallocated unit storage area among the unit storage areas included in the physical storage area to a write destination area for the write data in the virtual storage area, and

in a case where it is determined that the primary cache lacks a free area,

selecting write-back-target data from the primary cache,

saving the selected write-back-target data into a secondary cache in a case where a second unit storage area allocated to a second storage area being a write destination area for the selected write-back-target data in the virtual storage area is an area for which the overwrite processing has not been completed,

releasing a third storage area in the primary cache in which the selected write-back-target data was stored, and

write the write data to the released third storage area to respond to the write request.

2. The storage control apparatus according to claim 1 , wherein the processor is configured to manage the one or more first unit storage areas as unallocated unit storage areas.

3. The storage control apparatus according to claim 1 , wherein the processor is configured to:

determine whether the overwrite processing for the second unit storage area has been completed, at a timing asynchronous with the saving of the selected data into the secondary cache, and

perform a write-back of the selected data to the second unit storage area if it is determined that the overwrite processing has been completed.

4. The storage control apparatus according to claim 1 , wherein the processor is configured to:

when it is determined that the secondary cache lacks a free area, select read cache data staged from the physical storage area among pieces of data stored in the secondary cache,

delete the read cache data from the secondary cache, and

write the selected data to an area in the secondary cache released by the deletion.

5. The storage control apparatus according to claim 1 , wherein the processor is configured to:

when the second unit storage area is an area on which the overwrite processing has been executed or an area which is not subject to the overwrite processing, perform a write-back of the selected data to the second unit storage area and releasing the second storage area in the primary cache, and

write the write data to the released second storage area and responding to the write request.

6. A non-transitory computer-readable storage medium storing a program that causes a computer to execute a process, the process comprising:

receiving a release request for a first storage area in a virtual storage area;

in response to the receiving of the release request for the first storage area, releasing, among unit storage areas included in a physical storage area, one or more first unit storage areas allocated to the first storage area from the first storage area to manage each of the released one or more first unit storage areas as an unallocated unit storage area;

executing overwrite processing of writing 0 to each of the released one or more first unit storage areas at a timing asynchronous with a response to the release request for the first storage area; and

in response to a write request to store write data to the virtual storage area, executing write processing including:

allocating the unallocated unit storage area among the unit storage areas included in the physical storage area to a write destination area for the write data in the virtual storage area, and

in a case where it is determined that the primary cache lacks a free area,

selecting write-back-target data from the primary cache,

saving the selected write-back-target data into a secondary cache in a case where a second unit storage area allocated to a second storage area being a write destination area for the selected write-back-target data in the virtual storage area is an area for which the overwrite processing has not been completed,

releasing a third storage area in the primary cache in which the selected write-back-target data was stored, and

write the write data to the released third storage area to respond to the write request.

7. The non-transitory computer-readable storage medium according to claim 6 , the process comprising managing the one or more first unit storage areas as unallocated unit storage areas.

8. The non-transitory computer-readable storage medium according to claim 6 , wherein the process comprises:

determining whether the overwrite processing for the second unit storage area has been completed, at a timing asynchronous with the saving of the selected data into the secondary cache; and

performing a write-back of the selected data to the second unit storage area if it is determined that the overwrite processing has been completed.

9. The non-transitory computer-readable storage medium according to claim 6 , wherein the write processing includes:

when it is determined that the secondary cache lacks a free area, selecting read cache data staged from the physical storage area among pieces of data stored in the secondary cache;

deleting the read cache data from the secondary cache; and

writing the selected data to an area in the secondary cache released by the deletion.

10. The non-transitory computer-readable storage medium according to claim 6 , wherein the write processing includes:

when the second unit storage area is an area on which the overwrite processing has been executed or an area which is not subject to the overwrite processing, performing a write-back of the selected data to the second unit storage area and releasing the second storage area in the primary cache; and

writing the write data to the released second storage area and responding to the write request.