1. A computer readable record medium on which a duplication combination management program for determining a combination of storage apparatus between which data duplication is performed is recorded, the program making a computer function as: a simultaneous failure occurrence degree storage section which stores a simultaneous failure occurrence degree; a manufacture date information acquisition section which acquires manufacture date information set as numeric values corresponding to dates of manufacture of a plurality of storage apparatus from the plurality of storage apparatus; a simultaneous failure occurrence degree calculation section which calculates a difference between numeric values indicative of the manufacture date information for each combination of two storage apparatus on the basis of the manufacture date information acquired by the manufacture date information acquisition section, calculates a simultaneous failure occurrence degree a value of which becomes smaller with an increase in the difference between the numeric values indicative of the manufacture date information, and stores the simultaneous failure occurrence degree in association with each combination of two storage apparatus in the simultaneous failure occurrence degree storage section; a combination pattern generation section which combines two of the plurality of storage apparatus, and generates a plurality of combination patterns; a simultaneous failure occurrence degree adding section which acquires simultaneous failure occurrence degrees corresponding to combinations of storage apparatus for each of the plurality of combination patterns generated by the combination pattern generation section from the simultaneous failure occurrence degree storage section, and calculates a total of the simultaneous failure occurrence degrees acquired; a duplication combination pattern determination section which determines that a combination pattern for which the total of the simultaneous failure occurrence degrees calculated by the simultaneous failure occurrence degree adding section 1 s the smallest is a duplication combination pattern; and a mirroring instruction section which sends a mirroring section that performs mirroring by the use of the plurality of storage apparatus instructions to perform mirroring by the use of combinations of two storage apparatus indicated in the duplication combination pattern determined by the duplication combination pattern determination section.