Initial copy operation, Figure 2 adding a pair in bc, Update copy operation – HP XP Business Copy Software User Manual

Page 17: 2 adding a pair in bc

Initial copy operation

This operation occurs when you create a new volume pair (see Figure 2). The BC initial copy operation

copies all data on the P-VOL to the associated S-VOL. The P-VOL remains available to all hosts for read and

write I/Os throughout the initial copy operation. After the initial copy is complete, the update copy

operation duplicates write operations performed on the P-VOL during the initial copy operation at the

S-VOL.
Before the initial copy operation, the status of a pair is SMPL. The status of the pair is COPY(PD)

(PD = pending) while the initial copy operation is in progress. The status changes to PAIR when the initial

copy is complete. Write operations performed on the P-VOL during the initial copy operation are

duplicated at the S-VOL by update copy operations after the initial copy is complete.

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.

illustrates an update copy operation in a BC pair

with only one S-VOL.

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.

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