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Disk Media Management
396 C141-C013
7.4 Background Media Scan (BMS)
7.4.1 Overview
This function performs a background task that verifies the entire media surface by
scanning it during idle time based on the specification on Mode Page 0x1C
SubPage 0x01 (Background Control mode Page). During the scan, automatic
alternate processing is performed based on what is specified by the Retry
Parameter. This function thus makes it possible to detect sectors early that are
likely to become bad sectors and take appropriate countermeasures.
If another command is issued during the scan, that command is executed
immediately to ensure that the status information during the scan, the LBA that
encountered the error, and other information can be read on Log Page 0x15.
7.4.2 Background Media Scan
The Background Media Scan function can be performed in either of the following
two modes:
• Background Media Scan (BMS) mode
• Pre-Scan mode
The subsequent sections explain both modes in detail.
7.4.2.1 Background Media Scan (BMS) mode
In this mode, the entire media surface is verified. Once one verification operation
ends (either normally or midway with an error), a verification operation can be
repeated after the BMS Interval Time.
When the previous verification operation ended normally, the next verification
operation will begin with LBA 0.
If the previous verification operation ended with an error amid LBAs, the next
verification operation will begin with the LBA that is next to the LBA that
encountered the error.
7.4.2.2 Pre-Scan mode
In this mode, the entire media surface is verified immediately after power-on
(Spin-Up). Once a scan ends (with normal end of entire surface verification or
with an error), a scan in this mode will not begin until the following operation is
performed:
1) The Mode Page EN_PS bit is cleared to '0.'
2) The Mode Page EN_PS bit is set to '1.'
3) Power on/off is performed.