SMART Disk Drives Warn You Before They Fail

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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
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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