Product manual

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Chapter 7: Technology Background
This chapter covers the following topics:
• Disk Arrays (below)
• Logical Drives (page 261)
• Spare Drives (page 283)
• RAID Controllers (page 289)
Disk Arrays
Media Patrol
Media Patrol is a routine maintenance procedure that checks the magnetic media
on each disk drive. Media Patrol checks all physical drives assigned to disk
arrays and spare drives. Media Patrol does not check unconfigured drives.
Media Patrol checks are enabled by default on all disk arrays and spare drives.
You can disable Media Patrol in the disk array and spare drive settings, however
that action is not recommended.
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 on the disk
array.
Media Patrol has three status conditions:
• Running – Normal. You can access your logical drives at any time.
• Yield – Temporary pause while a read/write operation takes place.
• Paused – Temporary pause while another background runs. Or a pause
initiated by the user.
See “Running Media Patrol on a Disk Array” on page 129
PDM
Predictive Data Migration (PDM) is the migration of data from the suspect disk
drive to a spare disk drive, similar to rebuilding a logical drive. But unlike
Rebuilding, PDM constantly monitors your disk drives and automatically copies
your data to a spare disk drive BEFORE the disk drive fails and your logical drive
goes Critical.
The following actions trigger PDM:
• A disk drive with unhealthy status (see below)
• Media Patrol finds a disk critical error