HP StorageWorks XP24000 User Manual page 19

Figure 7 (page 19) illustrates how the data changes during the backward pairresync operations.
Figure 7 Backward Pairresync Operations
The S-VOL remains fully accessible during a normal/quick resync operation, but becomes
inaccessible to all hosts during a reverse copy or quick restore operation.
When reverse copy or quick restore is in progress, you cannot perform, add, split, or resync pair
for any other pair that shares the same S-VOL (delete pair and suspend pair are allowed).
Pairresync operation time depends on the pair status, split or suspend. The relation between the
pair status and the time required for pairresync operations are as follow:
Pairresync for split pair
When a normal/quick resync operation is performed on a split pair, the XP storage system
copies all differential data from the S-VOL to the T-VOL. When a reverse copy or quick restore
operation is performed on a split pair, the storage system copies all differential data from the
ShadowImage for Mainframe Operations 19