If IEHMOVE is unable to successfully move or copy specified data, it tries to reorganize the data and place it on the specified output device. The reorganized data (called an unloaded data set) is a sequential data set consisting of 80-byte blocked records that contain the source data and control information for subsequently reconstructing the source data as it originally existed.

When an unloaded data set is moved or copied (via IEHMOVE) to a device that will support the data in its true form, the data is automatically reconstructed. For example, if you try to move a partitioned data set to a tape volume, the data is unloaded to that volume. You can re-create the data set merely by moving the unloaded data set to a DASD volume.