Storage system and storage control method

1. A storage system comprising:

a processor configured to produce a secondary volume (SVOL) which is a snapshot of a primary volume (PVOL),

wherein a data store volume (DSVOL) for a snapshot group which is a group of the PVOL and one or more SVOLs for the PVOL is a data storage region where data of which a storage destination is one volume (VOL) of the snapshot group and meta-information of the data are stored, and the meta-information is information including address mapping between a reference source address which is an address of a position of the data in the snapshot group and a reference destination address which is an address of a position of the data in the DSVOL,

wherein the processor executes I/O for updating the meta-information of data in a write process which is a process of a write request for updating the data in one VOL of the snapshot group with respect to the DSVOL storing meta-information, and

wherein the processor

determines whether an input/output (I/O) load on the snapshot group exceeds a threshold, and

increases the number of DSVOLs for the snapshot group when a determination result is positive.

2. The storage system according to claim 1 , wherein the processor equalizes amounts of data stored in a plurality of DSVOLS for the snapshot group.

3. The storage system according to claim 2 , wherein, in a process of a write request for one VOL of the snapshot group, the processor selects a DSVOL of a storage destination of a write target data which is data incidental to the write request and stores the write target data in the selected DSVOL so that the amounts of data stored in the plurality of DSVOLs are equalized.

4. The storage system according to claim 2 ,

wherein the equalization of the amounts of the data stored in the plurality of DSVOLs includes movement of data between the DSVOLs, and

wherein the processor executes asynchronously the equalization with the process of a I/O request for one VOL of the snapshot group.

5. The storage system according to claim 1 , wherein, after the number of DSVOL is increased for the snapshot group, the processor controls an amount of data of which a storage destination is a DSVOL existing before the increase in the number of DSVOLs and an amount of data of which a storage destination is a newly increased number of DSVOLS.

6. The storage system according to claim 5 , wherein, when there is an upper limit in the number of DSVOLs for the snapshot group, the processor controls an amount of data of which a storage destination is a DSVOL existing before the increase in the number of DSVOLs and an amount of data of which a storage destination is a newly increased number of DSVOLS.

7. The storage system according to claim 1 , wherein the case in which the input/output load on the snapshot group exceeds the threshold corresponds to one or both of:

a case in which a sum of I/O loads on all VOLs in the snapshot group exceeds an I/O load threshold determined for the snapshot group; and

a case in which for each of N or more DSVOLs (where N is a natural number) among all the DSVOLs allocated to the snapshot group, an I/O load of the DSVOL exceeds expected I/O performance of the DSVOL.

8. The storage system according to claim 7 , wherein the I/O load threshold determined for the snapshot group is a product of I/O performance expected in one DSVOL and a current number of DSVOLs which is the number of DSVOL allocated to the snapshot group or a value less than the product.

9. The storage system according to claim 1 ,

wherein the processor determines a newly increased number of DSVOLs based on a difference between a target number and a current number of DSVOLs in the snapshot group,

wherein the current number of DSVOLs is the number of DSVOL allocated to the snapshot group, and

wherein the target number is the number of DSVOLS of which an I/O load on the snapshot group is equal to or less than the threshold.

10. The storage system according to claim 9 , wherein the newly increased number of DSVOLs is a number which is based on the difference and the current number of DSVOLS and is greater than the difference.

11. The storage system according to claim 10 , wherein the newly increased number of DSVOLs is a number in which an I/O load on one DSVOL in the snapshot group is kept equal to or less than an expected I/O performance of the DSVOL.

12. The storage system according to claim 1 , further comprising:

a plurality of storage controllers,

wherein each of the plurality of storage controllers includes the processor,

wherein an I/O right of the plurality of DSVOLs in the snapshot group is distributed, and

wherein each of the plurality of storage controllers stores data in the DSVOL for which the storage controller has the I/O right, and

transfers the data to the storage controller having the I/O right when the storage controller does not have the I/O right of the DSVOL serving as a storage destination of the data.

13. A storage control method of a storage system producing a secondary volume (SVOL) which is a snapshot of a primary volume (PVOL),

wherein a data store volume (DSVOL) for a snapshot group which is a group of the PVOL and one or more SVOLs for the PVOL is a data storage region where data of which a storage destination is one volume (VOL) of the snapshot group and meta-information of the data are stored, and the meta-information is information including address mapping between a reference source address which is an address of a position of the data in the snapshot group and a reference destination address which is an address of a position of the data in the DSVOL,

wherein the storage system executes I/O for updating the meta-information of data in a write process which is a process of a write request for updating the data in one VOL of the snapshot group with respect to the DSVOL storing meta-information, and

wherein the storage control method comprises:

determining whether an input/output (I/O) load on the snapshot group exceeds a threshold, and

increasing the number of DSVOLS for the snapshot group when the determination result is positive.