I was just perusing through some technical notes and ran into a brief writeup on OMEGAMON Storage and its interplay with RMF. The bottom line is OMEGAMON Storage collects its device information from RMF (among other places). As part of the collection setup you may specify a collection interval which can control how often information is gathered and potentially stored by the tool.
One of the options for the collection interval is RMF, whch means the tool will collect by default on the same interval as RMF. If your RMF interval is something like 15 minutes (common in many shops), then this will usually work fine. However, if you you have a smaller RMF interval, then you may want to apply some more thought to the collection interval. Collecting on a narrower interval, and therefore more frequently may result in more collection overhead.
Here's a link to the note: