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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.
CAUTION:
Even if a copy operation is completed without any host I/O, the data in the P-VOL and S-VOL may not
beidentical.WhethertheP-VOLandtheS-VOLhavethesamedatadependsontheconditionofthe
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.
TheslowerpaceminimizestheimpactofBCoperationsondiskarrayI/Operformance,whilethefaster
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 i
s 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
copyoperationinaBCpairwithonlyoneS-VOL.
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Business Copy XP (BC) for the Array