Storage device and storage method

A computer-implemented storage method comprising:

• determining, in accordance with an amount of dirty data stored in a cache memory, the dirty data being not written back to a nonvolatile storage device, a first physical volume and a first logical volume placed in the first physical volume from the plurality of physical volumes and the plurality of logical volumes placed in the plurality of physical volumes;
• selecting, from a first plurality of physical volumes in which the determined first logical volume is placed by mirroring, a second physical volume other than the determined first physical volume as a read source, and selecting, from the plurality of physical volumes, a third physical volume other than the second plurality of physical volumes as a write destination;
• and
• writing data of the first logical volume read from the second physical volume selected as the read source, to the third physical volume selected as the write destination, and deleting the first logical volume from the determined first physical volume.

A non-transitory computer-readable medium storing instructions executable by one or more computers, the instructions comprising:

• one or more instructions for determining, in accordance with an amount of dirty data stored in a cache memory, the dirty data being not written back to a nonvolatile storage device, a first physical volume and a first logical volume placed in the first physical volume from the plurality of physical volumes and the plurality of logical volumes placed in the plurality of physical volumes;
• one or more instructions for selecting, from a first plurality of physical volumes in which the determined first logical volume is placed by mirroring, a second physical volume other than the determined first physical volume as a read source, and selecting, from the plurality of physical volumes, a third physical volume other than the second plurality of physical volumes as a write destination;
• and
• one or more instructions for writing data of the first logical volume read from the second physical volume selected as the read source, to the third physical volume selected as the write destination, and deleting the first logical volume from the determined first physical volume.