Promise Technology VTRAK M610p, Руководство по эксплуатации продукта

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Chapter 7: Technology Background
209
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 48 (WebPAM PROe) or page 122 (CLU).
You can also run Media Patrol on a disk array. See “Running Media Patrol on a
Disk Array” on page 102 (WebPAM PROe) or page 139 (CLU).
Predictive Data Migration (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. See “Running PDM” on page 48 for WebPAM PROe or page 141
for the CLU.
After the data is copied from the suspect disk drive, the controller marks it with a
Stale configuration and a PFA error.
You can clear the Stale configuration and PFA error and put the disk drive back
into service. See “Clearing Stale and PFA Conditions” on page 89 for WebPAM
PROe or page 131 for the CLU. In some cases, however, you might remove the
disk drive for repair or replacement.
PDM Triggers
The following actions trigger PDM:
• A disk 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 disk 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 disk drive creates a map around it. These maps are saved in the
bad sector remapping table, which has a capacity of 512 reassigned blocks and
1024 error blocks.