Document the three numbers shown from the Counter

The three-value counter has been a mystery to interpret. An example of the counter value is `StorageMetrics`'s field like this `BytesInput="606.399 2618.63 12306012486"`.

Now I know the meaning is:
The first one is rate, the second one is roughness, the third one is the absolute value.

But where should we document the metrics and anything that is related to operation?

Start by locating the documentation for StorageMetrics and the three-value counter. Document the meanings of rate, roughness, and absolute value, along with the related operation guidance requested in the issue; done means a reader can interpret values such as BytesInput="606.399 2618.63 12306012486".

Written by the indexing model from the issue text.