The spanning feature of BDAM lets you create and process variable-length unblocked logical records that span tracks. The feature also lets you pack tracks with variable-length records by splitting the records into segments. Figure 1 shows how these segments can then be written onto more than one track.

Figure 1. Spanned Format-V Records for Direct Data Sets

When you specify spanned, unblocked record format for the basic direct access method, and when a complete logical record cannot fit on the track, the system tries to fill the track with a record segment. Thus, the maximum record length of a data set is not restricted by track capacity. Segmenting records permits a record to span several tracks, with each segment of the record on a different track. However, because the system does not permit a record to span volumes, all segments of a logical record in a direct data set are on the same volume.

Recommendation: Do not use the basic direct access method (BDAM).