HP XP Business Copy Software - Manual (Page 22)

22 Business Copy XP (BC) for the XP10000/XP12000
CAUTION: If a copy operation is completed without any host I/O, the data in the P-VOL and S-VOL may
not be the same. 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.
NOTE: When creating pairs, you can select the pace for the initial copy operation: slower, medium, and
faster. The slower pace minimizes the impact of BC operations on disk array I/O performance, while the
faster pace completes the initial copy operation as quickly as possible.
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: If a copy operation is completed without any host I/O, the data in the P-VOL and S-VOL may
not be the same. 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.
NOTE:
•
Update copy operations are not performed for pairs with the following status: COPY(PD) (pending
duplex), COPY(SP) (steady split pending), PSUS(SP) (quick split pending), PSUS (split), COPY(RS)
(resync), COPY(RS-R) (resync-reverse), and PSUE (suspended).
• Update copy operations do not occur every time a host issues a write I/O operation to the P-VOL of a
BC pair. BC update copy operations are performed asynchronously according to the differential
bitmap, which is stored in shared memory.