Managing a mass storage system that comprises a first and second storage space. A file index is generated listing each file along with a first characteristic quantity (FCQ), a second characteristic quantity (SCQ), and status information. Status information specifies if the file is held on the first or second storage space. A sample of files is selected from the file index containing a given number of files, wherein status information of each file specifies the first storage space. The FCQ of each file in the sample is used to determine the first critical value (FCV). The SCQ of each file in the sample is used to determine the second critical value (SCV). A first subset of files comprising each file where FCQ is larger than FCV, SCQ is larger than SCV, and specified by status information to be held on the first storage device is determined.