HP StorageWorks XP24000 User Manual page 11

Figure 2 Adding a Pair (Initial Copy)
Before the initial copy operation, the status of a pair is Simplex. The status of the pair is Pending
while the initial copy operation is in progress. The status changes to Duplex when the initial copy
is complete.
Write operations performed on the S-VOL during the initial copy operation will be duplicated at
the T-VOL by update copy operations after the initial copy is complete.
Since an S-VOL remains available to all hosts for read and write I/Os during the initial copy
operation, the S-VOL might be updated during the operation. Therefore, when the status of the
pair changes to Duplex after the initial copy operation is complete, the update copy operations
start and the differential data of the S-VOL is copied to the T-VOL. As write I/Os are performed
on a duplex S-VOL, the XP storage system stores the differential bitmap, and then performs update
copy operations periodically based on the amount of differential data present on the S-VOL as
well as the elapsed time between update copy operations. Figure 3 (page 12) illustrates an update
copy operation in a SIz pair with only one T-VOL.
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