HP XP Business Copy Software - Manual (Page 167)

ShadowImage for z/OS user guide 167
5 Unit used for pair
management
Pairs are managed by volume. Even
when multiple datasets on the same
volume are specified, the number of
pair is regarded as 1.
Pairs are managed by the specified
extents, or by volume when the entire
volume is specified. When multiple
datasets are specified on the same
volume, each dataset is regarded as a
pair.