Product manual

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Chapter 7: Technology Background
This chapter covers the following topics:
• Disk Arrays (below)
• Logical Drives (page 333)
• Spare Drives (page 355)
• RAID Controllers (page 361)
• iSCSI Management (page 366)
• Internet Protocols (page 373)
Disk Arrays
Disk array technology includes:
• Media Patrol (page 331)
• PDM (page 331)
• Power Management (page 332)
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 158.
PDM
Predictive Data Migration (PDM) is the migration of data from the suspect phyical
drive to a spare drive, similar to rebuilding a logical drive. But unlike Rebuilding,