Reduction of performance impacts of storage power control by migration of write-intensive extent

1. A method comprising:

monitoring a set of read operations and a set of write operations for a set of drives in a storage system during a first time window;

calculating, based on the monitoring, a write intensity of a first drive in the set of drives;

classifying, based on the write intensity, the first drive as a candidate for power reduction;

identifying, based on the monitoring, a write-intensive extent on the first drive;

migrating a read-intensive extent off a second drive to provide space for the write-intensive extent;

migrating the write-intensive extent to the second drive in the set of drives prior to reducing the power to the first drive to mitigate write-performance impacts of reducing power to the first drive; and

reducing power to the first drive.

2. The method of claim 1 , wherein the calculating comprises:

identifying a number of read operations performed by the first drive during the first time window;

identifying a number of write operations performed by the first drive during the first time window;

adding the number of read operations to the number of write operations, resulting in a number of total operations performed by the first drive during the first time window; and

dividing the number of write operations by the number of total operations resulting in a total write proportion for the first drive.

3. The method of claim 1 , wherein the calculating comprises:

identifying a number of extents that were write intensive during the first time window;

identifying a total number of extents in the first drive; and

dividing the number of write-intensive extents by the total number of extents, resulting in a write-extent proportion for the first drive.

4. The method of claim 1 , wherein the classifying comprises:

comparing the write intensity of the first drive to a maximum intensity threshold; and

determining that the write intensity is below the maximum intensity threshold.

5. The method of claim 4 , wherein the classifying further comprises:

comparing the write intensity of the first drive to a minimum intensity threshold; and

determining that the write intensity is above the minimum intensity threshold.

6. The method of claim 1 , wherein the migrating comprises:

performing a migration-read operation on the extent on the first drive;

performing a migration-write operation of the extent to the second drive; and

recording the migration-read operation and the migration-write operation as power-reduction-migration operations.

7. The method of claim 1 , wherein the monitoring comprises subtracting power-reduction-migration operations from the set of read operations and the set of write operations.

8. The method of claim 1 , wherein reducing power to the first drive disproportionately affects the performance of write operations on the drive more than read operations on the drive.

9. A system comprising:

a processor; and

a memory in communication with the processor, the memory containing program instructions that, when executed by the processor, are configured to cause the processor to perform a method, the method comprising:

monitoring a set of read operations and a set of write operations for a set of drives in a storage system during a first time window, wherein the monitoring comprises subtracting power-reduction-migration operations from the set of read operations and the set of write operations;

calculating, based on the monitoring, a write intensity of a first drive in the set of drives;

classifying, based on the write intensity, the first drive as a candidate for power reduction;

identifying, based on the monitoring, a write-intensive extent on the first drive;

migrating the write-intensive extent to a second drive in the set of drives prior to reducing the power to the first drive to mitigate write-performance impacts of reducing power to the first drive; and

reducing power to the first drive.

10. The system of claim 9 , wherein the method performed by the processor further comprises:

identifying a number of read operations performed by the first drive during the first time window;

identifying a number of write operations performed by the first drive during the first time window;

adding the number of read operations to the number of write operations, resulting in a number of total operations performed by the first drive during the first time window; and

dividing the number of write operations by the number of total operations resulting in a total write proportion for the first drive.

11. The system of claim 9 , wherein the calculating comprises:

identifying a number of extents that were write intensive during the first time window;

identifying a total number of extents in the first drive; and

dividing the number of write-intensive extents by the total number of extents, resulting in a write-extent proportion for the first drive.

12. The system of claim 9 , wherein the classifying comprises:

comparing the write intensity of the first drive to a maximum intensity threshold; and

determining that the write intensity is below the maximum intensity threshold.

13. The system of claim 9 , wherein the method performed by the processor further comprises:

migrating a read-intensive extent off the second drive to provide space for the write-intensive extent.

14. The system of claim 9 , wherein the method performed by the processor further comprises:

performing a migration-read operation on the extent on the first drive;

performing a migration-write operation of the extent to the second drive; and

recording the migration-read operation and the migration-write operation as power-reduction-migration operations.

15. A computer program product, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a computer to cause the computer to:

monitor a set of read operations and a set of write operations for a set of drives in a storage system during a first time window;

calculate, based on the monitoring, a write intensity of a first drive in the set of drives;

classify, based on the write intensity, the first drive as a candidate for power reduction;

identify, based on the monitoring, a write-intensive extent on the first drive;

migrate a read-intensive extent off a second drive to provide space for the write-intensive extent;

migrate the write-intensive extent to the second drive in the set of drives prior to reducing the power to the first drive to mitigate write-performance impacts of reducing power to the first drive; and

reduce power to the first drive.

16. The computer program product of claim 15 , wherein the program instructions further cause the computer to:

identify a number of read operations performed by the first drive during the first time window;

identify a number of write operations performed by the first drive during the first time window;

add the number of read operations to the number of write operations, resulting in a number of total operations performed by the first drive during the first time window; and

divide the number of write operations by the number of total operations resulting in a total write proportion for the first drive.

17. The computer program product of claim 15 , wherein the calculating comprises:

identifying a number of extents that were write intensive during the first time window;

identifying a total number of extents in the first drive; and

dividing the number of write-intensive extents by the total number of extents, resulting in a write-extent proportion for the first drive.

18. The computer program product of claim 15 , wherein the classifying comprises:

comparing the write intensity of the first drive to a maximum intensity threshold; and

determining that the write intensity is below the maximum intensity threshold.

19. The computer program product of claim 15 , wherein the monitoring comprises subtracting power-reduction-migration operations from the set of read operations and the set of write operations.

20. The computer program product of claim 15 , wherein the program instructions further cause the computer to:

perform a migration-read operation on the extent on the first drive;

perform a migration-write operation of the extent to the second drive; and

record the migration-read operation and the migration-write operation as power-reduction-migration operations.