When a storage subsystem logical drive is a primary logical drive and a full synchronization is necessary, the controller owner performs the 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. The synchronization priority defines how much processsing time is allocated for synchronization activities relative to system performance.
The following guidelines may help you determine how long a synchronization priority might take and how much various synchronization priorities can affect system performance.
Synchronization Priority Rates
The following priority rates are available.
Lowest
Low
Medium
High
Highest
Note: The Lowest priority rate favors system performance, but the full synchronization will take longer. The Highest priority rate favors the full synchronization, but system performance may be compromised. The following guidelines roughly approximate the differences between the five priorities. Logical Drive size and Host I/O rate loads affect the synchronization time comparisions.
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.
Viewing the Progress of a Full Synchronization
The Synchronization progress bar at the bottom of the Mirroring tab of the Logical Drive Properties dialog displays the progress of a full synchronization.