SATA-Disk Module 4
APSDMxxxx15XX-PXX
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© 2013 Apacer Technology Inc. Rev. 1.4
5.6 S.M.A.R.T.
S.M.A.R.T. is an abbreviation for Self-Monitoring, Analysis and Reporting Technology, a self-monitoring
system that provides indicators of drive health as well as potential disk problems. It serves as a warning
for users from unscheduled downtime by monitoring and displaying critical drive information. Ideally, this
should allow taking proactive actions to prevent drive failure and make use of S.M.A.R.T. information for
future product development reference.
Apacer devices use the standard SMART command B0h to read data out from the drive to activate our
S.M.A.R.T. feature that complies with the ATA/ATAPI specifications. S.M.A.R.T. Attribute IDs shall
include initial bad block count, total later bad block count, maximum erase count, average erase count,
power on hours and power cycle. When the S.M.A.R.T. Utility running on the host, it analyzes and reports
the disk status to the host before the device reaches in critical condition.
Note: attribute IDs may vary from product models due to various solution design and supporting
capabilities.
5.7 TRIM
TRIM, though in capital letters usually, is a memory computation command rather than an abbreviation. It
is mainly a SATA command that enables the operating system to inform the SSD (Solid State Drive)
which blocks of previously stored data are no longer valid, due to erases by the host or operating system,
such as file deletions or disk formatting. Once notified, SSD will begin the discard of the invalid LBAs and
retain more space for itself, in fact, the discarded is no longer recoverable.
When an LBA is replaced by the operating system, as with overwrite of a file, the SSD is informed that the
originally occupied LBA is determined as no longer in use or invalid. The SSD will not save those blocks
in garbage collected sectors. Noticeably, a file deletion command by host or operating system never
actually erases the actual content, rather, just the file is marked as deleted. This issue is even specifically
noticeable for flash based memory devices, such as SSDs. In fact, an SSD will keep garbage collecting
the invalid, previously occupied LBAs, if it is not informed that these LBAs can be erased. Thus, the SSD
would experience a significant performance downfall.
