Patent ID: 7603337

Claim:
A file management method of a storage system storing a plurality of files into a plurality of storage tiers based upon data importance and utilization frequencies, comprising: a step of managing a plurality of file groups each of which is related to an application used by a host unit and contains at least two of the files stored in different one of the tiers; a step of setting, for each of the file groups, at least one file belonging to said each file group and being stored in the uppermost one of the tiers as a file subject observation; a step of determining whether or not promotion conditions are satisfied when a specific action occurs for said file subject to observation; a step of promoting the other files belonging to the same file group as said file subject to observation to the uppermost tier in response to the specific action so that all files belonging to said file group can be used from start of the utilization, when promotion conditions are satisfied; a step of demoting the other files belonging to the same file group as said file subject to observation to the lowermost tier, when demotion condition are satisfied, wherein said file subject to observation is determined dynamically by referring to a table storing a condition of file subject to observation, comparing the present file subject to observation and the other files of each said file group, and switching from the present file subject to observation to the most appropriate file of each said file group which satisfies the condition as a new file subject to observation; a step of determining whether or not files satisfying demotion conditions exist based on time and a weighting coefficient pertaining to processing of the file attribute information for the files which are other than files subject to observation of said each file group; and a step demoting a file satisfying the demotion conditions to a tier of a lower order than a current tier when the file is determined to satisfy the demotion conditions.