Provided are a computer program product, system, and method for building a metadata index from source metadata records when creating a target volume for subsequent metadata access from the target volume. The device comprises a base having a top surface and a pair of housings each having an inner surface. The width of the unlocking zone is greater than the width of the locking zone and than the width of the slot, but less than or equal to the width of the setback, said widths being measured axially. Moreover, by using random numbers generation method, parameters are estimated by maximum likelihood method. The controller controls an operation of the sheet processing portion such that a width of a groove formed on a sheet located on an outer side of the folded sheet bundle is larger than that of a groove formed on a sheet located on an inner side of the folded sheet bundle.