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 61 for WebPAM PROe or page 164

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 112 for WebPAM

PROe or page 154 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.

When the table fills to a specified percentage of its capacity, PDM triggers a

migration of data from the suspect drive (the disk drive with the bad sectors) to a

spare disk drive.

During data migration, you will have access to the Logical Drive but it will respond

more slowly to read/write tasks because of the additional operation. The time

required for data migration depends on the size of the disk drive.

See “Making Background Activity Settings” on page 59 (WebPAM PROe) or

page 177 (CLU).


Note: Please reference the Vtrak E-Class User Manual to look reference page information.