Volume Pairs (P-Vols And S-Vols); Cascaded Pairs - HP StorageWorks P9000 User Manual

Figure 1 Business Copy configuration

Volume pairs (P-VOLs and S-VOLs)

A pair consists of the primary and secondary data volumes. Each P-VOL can be paired with up to
three S-VOLs. Thus, you can create three pairs using one P-VOL.
During most operations, the P-VOL remains available to the host for I/O operations. When the
P-VOL is updated, the new data, called differential data, is copied to the S-VOL regularly. Because
S-VOLs are updated asynchronously, the P-VOL and S-VOL may not be identical. S-VOLs 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."
6 Business Copy overview