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SuperTrak EX Series User Manual
184
Media Patrol
Media Patrol is a routine maintenance procedure that checks the magnetic media
on each physical drive. Media Patrol checks all physical drives assigned to disk
arrays and on spare drives. Media Patrol does not check unconfigured drives.
Unlike Synchronization and Redundancy Check, Media Patrol is concerned with
the condition of the media itself, not the data recorded on the media. If Media
Patrol encounters a critical error, it triggers PDM if PDM is enabled.
You can run Media Patrol from the subsystem. See “Running Media Patrol” on
page 110.
You can also run Media Patrol on a disk array. See “Running Media Patrol on a
Disk Array” on page 140.
Predictive Data Migration (PDM)
Predictive Data Migration (PDM) is the migration of data from the suspect
physical drive to a spare drive, similar to Rebuilding a Logical Drive. But unlike
Rebuilding, PDM constantly monitors your physical drives and automatically
copies your data to the spare drive before the suspect drive fails and your Logical
Drive goes Critical. See “Running PDM” on page 110 and “Running PDM on a
Disk Array” on page 140.
After the data is copied from the suspect drive, the controller marks the suspect
drive with a Stale configuration and a PFA error.
You can clear the Stale configuration and PFA error and put the physical drive
back into service. See “Clearing Stale and PFA Conditions” on page 125. In some
cases, however, you might remove the physical drive for repair or replacement.
PDM Triggers
The following actions trigger PDM:
• A physical drive with unhealthy status (see below)
• Media Patrol finds a disk critical error*
• You initiate PDM manually
*PDM also counts the number of media errors reported by Media Patrol.
A physical drive becomes unhealthy when:
• A SMART error is reported
• The bad sector remapping table fills to the specified level
Because data would be lost if written to a bad sector, when a bad sector is
detected, the physical drive creates a map around it. These maps are saved in