HP XP P9500 Storage - Manual (Page 11)

Figure 4 Update copy operation
Though pair status is PAIR, data in the primary and secondary volumes may not be the same
because update copying occurs asynchronously, and therefore later data exists in the P-VOL. You
can insure that primary and secondary volumes data are the same at a certain point in time, by
splitting pair.
Also, data in the primary volume and the data in the secondary volume may not be the same if a
copy operation is completed without host I/O. As mentioned above, the primary and secondary
volumes can be made the same by splitting the pair.
Initial and update copy operations 11