SMART basics

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SMART basics

Postby lik » Wed Apr 21, 2010 9:03 am

SMART basics

SMART is the abbreviation for "Self Monitoring And Reporting Technology". It is a standard interface protocol and set of the disk features that allows disk to check its status and report it to a host system. SMART information consists of "attributes", each one describing some particular aspect of drive condition. Some attributes may be designated "life-critical", which implies that the corresponding parameters are more important than other ones.

Three values are associated with each SMART attribute:

* "Normalized value", commonly referred to as just "value". This is a most universal measurement, on the scale from 0 (bad) to some maximum (good) value. Maximum values are typically 100, 200 or 253. Rule of thumb is: high values are good, low values are bad.
* "Threshold" - the minimum normalized value limit for the attribute. If the normalized value falls below the threshold, the disk is considered defective and should be replaced under warranty. This situation is called "T.E.C." (Threshold Exceeded Condition).
* "Raw value" - the value of the attribute as it is tracked by the device, before any normalization takes place. Some raw numbers provide valuable insight when properly interpreted. These cases will be discussed later on. Raw values are typically listed in hexadecimal numbers.

Most common SMART attributes reference

Note that not all of the attributes are present on all drives. Some attributes are of similar meaning (just counted differently), so only one of them will normally be monitored by the drive. Some require special sensors (e.g. temperature or G-loads monitoring). The decision about which attributes should be implemented is up to the drive vendor. Along the same lines the interpretation of raw values depends heavily on the manufacturer.

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