3Ware 3W-7410 - Escalade 7410 RAID Controller, Руководство пользователя

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accordingly. Background Media Scan is also designed to be minimally
intrusive to the normal controller performance.
Background Media Scan can provide early warning of a disk drive problem or
failure. For example, if the media scan encounters many error locations, this
may be an indication of excessive grown defects on the drive. For redundant
arrays, grown defects can be fixed early to maintain optimal redundancy for
the array.
Many sectors on a drive may not be used or checked for long periods of time.
Bad sectors may not be known until actual user data is written and then read
from these locations. By periodic scanning of the media, the disk drive
firmware is allowed to do corrective actions on problem areas on the disk and
can minimize the occurrence of uncorrectable read errors.
Background Media Scan is scheduled through 3DM. When the media scan is
activated, the controller firmware either starts the scan at the first drive with
the lowest port number or scans from when it was last deactivated. While
scanning, the controller issues normal read commands to the drive in a
sequential manner. When the controller is idle with no host commands, the
rate of the media scan is as fast as the drive can transfer data. When an error
from the drive is encountered, the controller typically will retry the command.
If there are cable CRC errors, there may be multiple retries including
downgrade of the UDMA mode. If the error persists and is repairable (e.g.,
ECC errors), an error notification is issued to indicate the problem. (See
“AEN 026h AEN_DRIVE_ECC_ERROR” on page 105.) If the disk drive is
part of a redundant array that is in a redundant state (not DEGRADED,
REBUILDING), then Dynamic Sector Repair automatically rewrites the
redundant data to the error location to force the drive to reallocate the error
location. A notification of repair is posted. The result is a restoration of drive
and data integrity; the primary and redundant data are again both valid.
After repairs, Background Media Scan continues on the same disk drive until
reaching the maximum logical block address on the drive. It then proceeds
onto the next disk drive available for scanning. When it reaches the last drive
(i.e., drive with the highest port number), it stops until the next scheduled
scan. It will then start from the first drive.