Q:

How does rrdtool RRDB associate/bind an RRA to a DS?

How does rrdtool RRDB associate/bind an RRA to a DS? An XML dump does not seem to reveal where this binding info is kept. Neither does rrdinfo. But this info must be in there, because multiple RRAs can be associated with a single DS. Perhaps Am  I missing something?

A:

Every DS is in every RRA.  You do not need to bind a specific DS to specific RRAs as the vector created from the set of DS is common to all.
The difference between RRAs is not that they have a different DS vector, but that they have different lengths and granularities, and different roll-up functions.  This enables the RRA to pre-calculate summary data at storage time, so that at graph time, most of the work is already done, speeding up the process.

