How to read HDD SMART values

[cparke]

Example:

[05] Reallocated Sector Count:          141/140, Worst: 141 (Data = 467,0)

I think this means the hard drive has encountered 467 bad sectors and reallocated them. Is that correct?

But then what does the "141/140, Worst 141" mean? I think these are counters of some kind, but it's still pretty cryptic to me what it means.

All the SMART values are reported this way, could we really use a clear explanation of how to read all these values.

 

[Martin]

Yes, it's correct that this means 467 bad sectors were reallocated.
141/140 is the actual "normalized" value for this attribute - 141 the actual value, 140 the threshold value. When the actual value falls below the threshold it means there's a problem.
Worst is the lowest/worst value encountered by the drive during its lifetime.

 

[cparke]

That really could be made a bit more clearer, just throwing a fraction in someone's face is not intelligible.

And is it true that every manufacturer's algorithm for these various normalized values is proprietary and unpublished? I really wonder if the 141 will rise over time if no more bad sectors are encountered.

 

[Callistemon]

Is the Current Pending Sector Count above 0? While the Reallocated Sector Count may be fine if it stops increasing, the Current Pending Sector Count should always be 0.

The normalized values are scores. Most start at 100, but some start higher. Unlike with Error Rates, which can be diluted by future operation with less errors, normalized scores for Error Counts never increase even if errors stop occurring. The algorithm for calculating normalized scores is proprietary and unpublished. However, it can be observed that normalized values for Error Counts do not increase.

Many of the firmware thresholds make no sense. For example, it is considered critical if the Reallocated Sector Count is too high, but the Current Pending Sector Count can be infinitely high without warning. One of the main concerns of a high successful Reallocated Sector Count is that it indicates more reallocations may occur, which in turn might be unsuccessful. If an indirect indication of something else possibly occurring next is critical, then why isn't it critical when that something else actually occurs?