Creating a buffer point-in-time copy relationship for a point-in-time copy function executed to create a point-in-time copy relationship

1. A method of operating a copy function to create a point-in-time copy relationship, comprising:

initiating a point-in-time copy function to create a new point-in-time copy relationship from a source volume comprising a first volume to a target volume comprising a second volume;

detecting that the target volume of the new point-in-time copy relationship is a source volume of a first pre-existing point-in-time copy relationship having as a target volume a third volume;

detecting that the target volume of the first pre-existing point-in-time copy relationship is a source volume of a second pre-existing point-in-time copy relationship having as a target volume a fourth volume; and

creating a buffer point-in-time copy relationship having a source volume comprising the target volume of the first pre-existing relationship and a target volume comprising a fifth volume in response to detecting that the target volume of the new point-in-time copy relationship is the source volume of the first pre-existing point-in-time copy relationship and detecting that the target volume of the first pre-existing point-in-time copy relationship is the source volume of the second pre-existing point-in-time copy relationship, wherein the creating the buffer point-in-time copy results in a cascade of the first volume to the second volume, the second volume to the fifth volume, the fifth volume to the third volume, and the third volume to the fourth volume.

2. The method of claim 1 , wherein data in the source volumes in the point-in-time copy relationships are copied to the corresponding target volumes in the point-in-time copy relationships in response to an update to the source volumes while the source volumes and the target volumes are in the point-in-time copy relationship.

3. The method of claim 2 , wherein the point-in-time copy function comprises a FlashCopy function and wherein the point-in-time copy relationships comprise FlashCopy relationships.

4. The method of claim 1 , further comprising:

receiving a data write to the first volume;

performing a corresponding data read of the second volume; and

performing a data write to the fifth volume of the data read from the second volume.

5. The method of claim 4 , further comprising:

completing the data write to the first volume in response to performing a corresponding data read of the first volume and performing a data write to the second volume.

6. The method of claim 4 , further comprising:

performing a data write on the third volume comprising the target volume of the first pre-existing point-in-time copy relationship of the data written to the fifth volume.

7. The method of claim 1 , further comprising:

performing as a background copy operation after data written to the first volume is written to the fifth volume, writing data written to the fifth volume to the third volume in the first pre-existing point-in-time copy relationship and writing data written to the third volume to the fourth volume in the second pre-existing point-in-time copy relationship.

8. The method of claim 1 , further comprising:

removing the buffer point-in-time copy relationship in response to detecting that the first or second point-in-time copy relationship has stopped or completed the copy function.

9. A system, comprising:

a plurality of storage volumes including a first, second, third, fourth and fifth volumes; and

a storage volume controller connected to the volumes, the storage controller operated to perform:

initiating a point-in-time copy function to create a new point-in-time copy relationship from a source volume comprising a first volume to a target volume comprising a second volume;

detecting that the target volume of the new point-in-time copy relationship is a source volume of a first pre-existing point-in-time copy relationship having as a target volume the third volume;

detecting that the target volume of the first pre-existing point-in-time copy relationship is a source volume of a second pre-existing point-in-time copy relationship having as a target volume the fourth volume; and

creating a buffer point-in-time copy relationship having a source volume comprising the target volume of the first pre-existing relationship and a target volume comprising the fifth volume in response to detecting that the target volume of the new point-in-time copy relationship is the source volume of the first pre-existing point-in-time copy relationship and detecting that the target volume of the first pre-existing point-in-time copy relationship is the source volume of the second pre-existing point-in-time copy relationship, wherein the creating the buffer point-in-time copy results in a cascade of the first volume to the second volume, the second volume to the fifth volume, the fifth volume to the third volume, and the third volume to the fourth volume.

10. The system of claim 9 , wherein data in the source volumes in the point-in-time copy relationships are copied to the corresponding target volumes in the point-in-time copy relationships in response to an update to the source volumes while the source volumes and the target volumes are in the point-in-time copy relationship.

11. The system of claim 10 , wherein the point-in-time copy function comprises a FlashCopy function and wherein the point-in-time copy relationships comprise FlashCopy relationships.

12. The system of claim 9 , wherein the operations further comprise:

receiving a data write to the first volume;

performing a corresponding data read of the second volume; and

performing a data write to the fifth volume of the data read from the second volume.

13. The system of claim 12 , wherein the operations further comprise:

completing the data write to the first volume in response to performing a corresponding data read of the first volume and performing a data write to the second volume.

14. The system of claim 12 , wherein the operations further comprise:

performing a data write on the third volume comprising the target volume of the first pre-existing point-in-time copy relationship of the data written to the fifth volume.

15. The system of claim 9 , wherein the operations further comprise:

performing as a background copy operation after data written to the first volume is written to the fifth volume, writing data written to the fifth volume to the third volume in the first pre-existing point-in-time copy relationship and writing data written to the third volume to the fourth volume in the second pre-existing point-in-time copy relationship.

16. The system of claim 9 , wherein the operations further comprise:

removing the buffer point-in-time copy relationship in response to detecting that the first or second point-in-time copy relationship has stopped or completed the copy function.

17. A computer program product on a computer readable storage medium for operating a point-in-time copy function with respect to a first volume, second volume, third volume, fourth volume, and fifth volume, the product comprising instructions executed to cause operations, the operations comprising:

initiating a point-in-time copy function to create a new point-in-time copy relationship from a source volume comprising a first volume to a target volume comprising a second volume;

detecting that the target volume of the new point-in-time copy relationship is a source volume of a first pre-existing point-in-time copy relationship having as a target volume the third volume;

detecting that the target volume of the first pre-existing point-in-time copy relationship is a source volume of a second pre-existing point-in-time copy relationship having as a target volume the fourth volume; and

creating a buffer point-in-time copy relationship having a source volume comprising the target volume of the first pre-existing relationship and a target volume comprising the fifth volume in response to detecting that the target volume of the new point-in-time copy relationship is the source volume of the first pre-existing point-in-time copy relationship and detecting that the target volume of the first pre-existing point-in-time copy relationship is the source volume of the second pre-existing point-in-time copy relationship, wherein the creating the buffer point-in-time copy results in a cascade of the first volume to the second volume, the second volume to the fifth volume, the fifth volume to the third volume, and the third volume to the fourth volume.

18. The computer program product of claim 17 , wherein data in the source volumes in the point-in-time copy relationships are copied to the corresponding target volumes in the point-in-time copy relationships in response to an update to the source volumes while the source volumes and the target volumes are in the point-in-time copy relationship.

19. The computer program product of claim 18 , wherein the point-in-time copy function comprises a FlashCopy function and wherein the point-in-time copy relationships comprise FlashCopy relationships.

20. The computer program product of claim 17 , wherein the operations further comprise:

receiving a data write to the first volume;

performing a corresponding data read of the second volume; and

performing a data write to the fifth volume of the data read from the second volume.

21. The computer program product of claim 20 , wherein the operations further comprise:

completing the data write to the first volume in response to performing a corresponding data read of the first volume and performing a data write to the second volume.

22. The computer program product of claim 20 , wherein the operations further comprise:

performing a data write on the third volume comprising the target volume of the first pre-existing point-in-time copy relationship of the data written to the fifth volume.

23. The computer program product of claim 17 , wherein the operations further comprise:

performing as a background copy operation after data written to the first volume is written to the fifth volume, writing data written to the fifth volume to the third volume in the first pre-existing point-in-time copy relationship and writing data written to the third volume to the fourth volume in the second pre-existing point-in-time copy relationship.

24. The computer program product of claim 17 , wherein the operations further comprise:

removing the buffer point-in-time copy relationship in response to detecting that the first or second point-in-time copy relationship has stopped or completed the copy function.