1. A storage system comprising: a node; and a plurality of storage devices coupled to the node, said storage devices store data of files, wherein the node includes: a file attribute detecting module that detects file attributes of a plurality of file attribute items from a file that is to be allocated, a file allocation rule information storing unit that stores a plurality of file allocation rules which are selectively applied for allocating files to the storage devices, a file allocation rule selection policy storing unit that stores, for each of file attributes that is detected by the file attribute detecting module, at least a file allocation rule identifier identifying a file allocation rule that is to be applied in a process for allocating a file having the corresponding file attribute, and a file allocation control module that determines where said file to be allocated is to be stored in the storage devices, wherein said file attribute item that is detected by the file attribute detecting module are ranked into priority levels, and wherein said file allocation control module determines where said file to be allocated is to be stored, by extracting file allocation rule identifiers respectively corresponding to each of the file attributes that are detected by the file attribute detecting module, if the extracted file allocation rule identifiers includes a combination of file allocation rule identifiers contradicting one another, then selecting a file allocation rule identifier corresponding to a file attribute item ranked to a highest priority among the contradicting file allocation rule identifiers, and creating an actual file allocation rule composed of file allocation rules identified by not contradicting file allocation rule identifiers among the extracted file allocation rule identifiers and the selected file allocation rule identifier.