HP XP P9500 Storage - Manual (Page 8)

Figure 1 Business Copy configuration for Open and Mainframe
Volume pairs (primary volumes and secondary volumes)
A pair consists of the primary and secondary data volume and the volume. Each primary volume
(primary volume) can be paired with up to three secondary volumes (secondary volumes). Thus,
you can create three pairs using one primary volume.
During most operations, the primary volume remains available to the host for I/O operations.
When the primary volume is updated, the new data, called differential data, is copied to the
secondary volume regularly. Because secondary volumes are updated asynchronously, the primary
and secondary volumes may not be identical. secondary volumes become available for host access
only after the pair has been split or deleted.
Cascaded pairs
Each Business Copy S-VOL can be further paired with a second level S-VOL. A first level (L1) S-VOL
may be paired with two second level (L2) S-VOLs. Thus, up to nine S-VOLs can be available for
one P-VOL.
L2 pairs are referred to as “cascaded pairs”.
8 Business Copy overview