User Manual

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Vess R2000 Series Product Manual Promise Technologies
• Paused–Temporarypausewhileanotherbackground
runs.Orapauseinitiatedbytheuser.
PdM
Predictive Data Migration (PDM) is the migration of data from the suspect phyi-cal drive to a spare drive,
similar to rebuilding a logical drive. But unlike Re-building, 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nds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llstothespecied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 154 or “Managing Background
Activities” on page 143.
You can specify the maximum levels for the reassigned and error blocks in PDM settings. When the table lls
to a specied 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 194.