When the primary storage system accepts a host write operation for a P-VOL, the primary storage system performs an update copy operation to write the data on both the P-VOL and the S-VOL. The primary storage system does not accept another write operation for the P-VOL until it receives confirmation from the secondary storage system that the write operation was completed successfully on the S-VOL. This ensures that the data on the P-VOL and S-VOL remains synchronized.
Update copy operations have a higher priority than initial copy operations. However, if an initial copy operation is in progress when the host issues a write operation to a P-VOL, the update copy operation must wait until the completion of the number of tracks specified in the copy pace setting. For example, if the copy pace setting is 15 tracks, the update copy must wait until all 15 tracks (1 cylinder) in the initial copy operation are copied. At that time the update copy operation is performed, and then the initial copy operation is resumed.