HP XP Business Copy Software - Manual (Page 22)

Figure 2 Adding a pair in BC
.
Update copy operation
This operation updates the S-VOL of a BC pair after the initial copy operation is complete. Since a
P-VOL remains available to all hosts for read and write I/Os during the initial copy operation, the
P-VOL might be updated during the operation. Therefore, when the status of the pair changes to PAIR
after the initial copy operation is complete, the update copy operation takes place and the P-VOL's
differential data is copied to the S-VOL. Update copy operations take place only for duplex pairs
(status = PAIR). As write I/Os are performed on a duplex P-VOL, the disk array stores a map of the
P-VOL's differential data, and performs update copy operations periodically based on the amount of
differential data present on the P-VOL and the elapsed time between update copy operations.
Figure
3 illustrates an update copy operation in a BC pair with only one S-VOL.
CAUTION:
Even if a copy operation is completed without any host I/O, the data in the P-VOL and S-VOL may
not be identical. Whether the P-VOL and the S-VOL have the same data depends on the condition
of the disk array. To make the P-VOL and S-VOL data the same, split the pair and make the pair
status PSUS.
Business Copy XP (BC) for the Array 22