- Excel / Meridian Data Computer Drive User Manual

SECURSTOR ASTRA ES 101
You can also run Media Patrol on a disk array.
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.
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. 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.
Transition
The Transition feature enables you to specify ―permanent‖ spare drives for your Astra ES subsystem. Transition
is the process of replacing a revertible spare drive that is currently part of a disk array with an unconfigured
physical drive or a non-revertible spare. The revertible spare drive returns to its original status.
Transition happens automatically when the following sequence of events takes place:
• You create a revertible spare drive.
• A physical drive assigned to your disk array fails and the array goes critical or degraded.
• Astra ES automatically rebuilds your array to the revertible spare drive and the array becomes functional
again.
• You replace the failed physical drive with a new physical drive of equal or greater capacity.
• Astra ES automatically transitions (moves) the data from the revertible spare to the new physical drive.
• The new physical drive becomes part of the array and the revertible spare drive returns to its original spare
status.
Transition happens manually when you specify a different unconfigured physical drive to transition (move) the
data from the revertible spare drive.
See the example below.
Example