Product manual

VTrak E-Class Product Manual
332
PDM constantly monitors your physical drives and automatically copies your data
to a spare drive before the physical drive fails and your logical drive goes Critical.
The following actions trigger PDM:
• A phyical drive with unhealthy status (see below)
• Media Patrol finds a 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 physical 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 2048 error blocks. See “Making PDM Settings” on page 121 or “Making
Background Activity Settings” on page 273.
You can specify the maximum levels for the reassigned and error blocks in PDM
settings. When the table fills to a specified value, PDM triggers a migration of
data from the suspect drive (the disk drive with the bad sectors) to a replacement
physical drive.
During data migration, you have access to your logical drives but they respond
more slowly to read/write tasks because of the additional operation. The time
required for data migration depends on the size of the physical drives.
PDM is enabled on all disk arrays by default. You can disable PDM in the disk
array settings, however that action is not recommended.
See “Running PDM on a Disk Array” on page 159 or page 237.
Power Management
See “Power Saving” on page 364.