If you specify the extent when you establish a relationship, only a portion of the volume is copied. This is called dataset copying. Dataset copying establishes the relationship using the specified extent or extents. You can specify up to 16 target extents for one source extent. To perform dataset copying, the copy source extent must have the same number of tracks as the copy target extent.
Dataset copying can be performed when:
- The position of the copy source extent is different from the position of the copy target extent, and both extents are on the same volume.
- The copy source extent and the copy target extent are on different volumes.
- The copy source extent and the copy target extent do not overlap when they are on the same volume.
- The data in a single source extent will be copied simultaneously to multiple target extents.
- Volume copying is being performed using the same source volume.
- The number of overlapping extents in each overlapped area must be 16 or less.
Figure. Overlap of copy source extents
Dataset copying cannot be performed when:
- One of the copy target extents overlaps another copy target extent.
- One of the copy target extents overlaps a copy source extent.
- Establishing with an overlapping copy source extent and target extent for a copy target extent that already has a relationship.