Hi,
The simple answer is that agents don't report data to the MOM so MOM Smartstor only contains supportability metrics about the MOM itself or any metrics that could be generated directly on the MOM itself, normally through virtual agents (agentclusters.xml). Therefore Smartstor usage by MOM is generally very low, around 6000 live metrics so the historical count will generally not be much higher than that.
Each collector has its own Smartstor, so each collector will have historical data for all the agents that have reported to it, so you can expect almost all of your data to be coming from the combination of collectors.
When you are running a query for historical data, the MOM will be asking all of the collectors to return data they have for the particular agent/metric, which goes some way to show that if you have lots of historical data, you can expect a slower response in the Workstation.
There is a lot of information in the documentation about the best configuration for Smartstor, ideally, as the documentation will say, each EM should have Smartstor on a dedicated disk, you can check the bottom of the following page for a lot of guidelines in general about Smartstor and the whole of the EM infrastructure:
Enterprise Manager Cluster Sizing and Performance Considerations - CA Application Performance Management - 10.0 - CA Wik…
Thanks,
David