SMART Disk Drives Warn You Before They Fail
By Stephen Bucaro
Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) is a feature built-in
to modern hard drives that monitors certain parameters of their operation in an attempt
to provide a warning when failure is imminent. Some of the parameters typically monitored include:
• head floating height
• temperature
• spin-up time
• seek time
• seek error rate
• spare sector count
• data throughput
If any of these parameters fall outside the drive manufacturer's specifications, SMART
alerts the administrator, allowing them to back up the data and make provisions to replace
the drive before it fails.
Hard drive failures can be categorized as two types: unpredictable and predictable.
Not much can be done about unpredictable failures, such as those caused by a power surge.
But, because a disk drive is a mechanical device, its operating parameters degrade
over time. Monitoring these parameters can allow you to predict a potential failure.
An example of a measurable parameter is head floating height. If head floating height
starts to fall below the drive manufacturer's specifications, this would indicate the
potential for a head crash.
In SMARTs basic operation, the disk driver software polls sensors on the drive and if
a sensor indicates a parameter outside of the drive manufacturer's specifications the
driver sends an alert to the operating system, and the operating system sends an alert
to the user or administrator.
You might be wondering why SMART would monitor a drives spare sector count. Hard drives
have the ability to detect bad sectors. Even good hard drives occasionally get bad sectors
and when they identify a bad sector they mark it and replace it with a spare sector.
If the spare sector count drops too low, that indicates that the drive has used up
most of its spare sectors, so it will be unable allocate spare sectors to make repairs.
The requirements for SMART are a SMART capable hard drive, a BIOS with the SMART feature
enabled, a SMART driver, and an operating system that supports SMART. Operating systems
that support SMART are: Microsoft Windows (2000, XP, Vista, 2003) and Linux (kernel 2.4
and 2.6). On these systems SMART is supported for SATA and IDE disk drives.
At this time SMART sends an alert when a monitored parameter falls out of specification,
but it does not allow you to querie monitored parameters. However, there are many utilities
available that will generate reports of the status of SMART parameters.
The name given to this technology was an unfortunate choice because there's a myriad
of technologies that use the SMART acronym. There's an attempt to avoid the confusion
by using only S.M.A.R.T. as the acronym for Self-Monitoring, Analysis and Reporting Technology.
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