HP XP P9500 Storage - Manual (Page 12)

Update copy has a higher priority than initial copy. However, if an initial copy is in progress when
updates are sent by the host, the update copy must wait until the initial copy’s copy pace completes.
For example, if the copy pace is 15 tracks, the update copy may wait up to 15 tracks (1 cylinder).
12 Continuous Access Synchronous Z overview