Chapter 9. Maintaining Units156 3ware Serial ATA RAID Controller User GuideBackground Task PrioritizationAlthough migration tasks follow the same schedule as rebuild andinitialization tasks, they are always given the highest priority because of thecontroller and disk resources required during migration.Once a unit is put into the migration state, it must be allowed to complete theprocess. While migrating, rebuilds or verifies to the unit are not permitted.Rebuilding preempts verify operations. If a unit requires rebuilding, thatprocess will take place before the unit is verified.Controllers can work on multiple units at the same time. This means that ifyou have both a redundant unit and a non-redundant unit, the verification ofthe redundant unit and the media scan of the non-redundant unit will occur atthe same time.Scheduling Background TasksYou can set up scheduling windows for when background tasks occur so thatroutine maintenance of storage media occurs when it will be least likely tointerfere with day-to-day work on the system (peak I/O times). By creatingand using schedules, you can specify when active rebuilding, migrating,verifying, and testing of units should occur. For example, you might thesetasks to occur at 2AM each day, or on weekends.The initial schedule setting is to “Ignore Schedule.” This allows the controllerfirmware to automatically initiate background tasks.Rebuild/migrate, verify, and self-test tasks are scheduled separately, but in avery similar way. You can perform the following scheduling tasks:• Viewing Current Task Schedules• Turning On or Off Use of a Task Schedule• Removing a Task Schedule• Adding a New Task Schedule Slot• Selecting Self-tests to be PerformedNote: Initialization follows the rebuild/migrate schedule.
