The controller owner of a primary Logical Drive performs a full synchronization in the background while processing local I/O writes to the primary logical drive and associated remote writes to the secondary logical drive. Because the full synchronization diverts controller processing resources from I/O activity, it can have a performance impact to the host application.
You can choose from five different synchronization priorities for the primary controller owner, ranging from Lowest to Highest, that determines how much of a priority the full synchronization will be relative to host I/O activity, and therefore how much of a performance impact there will be. The following guidelines roughly approximate the differences between the five priorities. Note that logical drive size can cause these estimates to vary widely.
A full synchronization at the lowest synchronization priority rate will take approximately eight times as long as a full synchronization at the highest synchronization priority rate.
A full synchronization at the low synchronization priority rate will take approximately six times as long as a full synchronization at the highest synchronization priority rate.
A full synchronization at the medium synchronization priority rate will take approximately three and a half times as long as a full synchronization at the highest synchronization priority rate.
A full synchronization at the high synchronization priority rate will take approximately twice as long as a full synchronization at the highest synchronization priority rate.
You set the synchronization priority when you create the Remote Mirror, or you can change it later using the Change Synchronization Priority option. Although the primary controller owner performs the full synchronization and uses the synchronization priority, it is set for both the primary and secondary logical drives during Remote Mirror creation in case of a role reversal.