A data storage medium stories data in the form of marks, said marks being written and/or read by an array of probes. The storage medium further includes a plurality of data fields, each field including an area of the storage medium which, in use, is scanned for reading and/or writing by an associated one of the array of probes. The data fields include operational data fields having operational data for operating said scanning stored dierein, wherein the operational data fields are arranged in a plurality of clusters, each cluster including a plurality of adjacent operational data fields. The invention also provides a method of scanning the data storage medium with the probe array, in which a target data field is determined and an operational data cluster closest to the target data field is selected and the operational data stored therein is used to control parameters of the scanning.