Monday, 25 April 2011

Difference between raw data and interpretation

One should prefer to look at and to work with raw data, if at all possible.

We got an example recently when an owner complained on a hard drive because SpeedFan reported Fitness around 25%. This does not sound good. However, closer examination revealed that SpeedFan conclusion was based on an attribute with a value of 100 (raw value 0). There appeared to be no trouble at all from the raw SMART output. Upon further investigation I found that there are two versions of the firmware on the same model hard drive, one reporting a perfectly good condition as value 253 (raw 0), and the other reporting the same perfectly good condition as value 100 (raw 0). SpeedFan sees both values as originating from a single model, and decides 100 to be a failure indication.

The more complex interpretation becomes, the more suspectible it is to all sorts of quirks and glitches. Unfrotunately, the more complex interpretation requires more human effort to work from raw data, but that's another matter entirely.

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