Hi @shem,
Regarding performance impact of multiple collectors I have many customers who use both OPM and Harvest and have never heard about any perf hit using both tools. I also did some basic tests to see the impact of various collection frequencies on node CPU use. See here for more.
Regarding Harvest pulling perf data from OPM this is not something on the roadmap at the moment. If you want to use OPM as your data source that could be accomplished without Harvest using the OPM native Graphite push "external data provider" feature. Or, for more stats and flexibility, you could write some code that would poll API Services and then submit the results to a metrics store of your choice. At the time Harvest was created the API Services feature wasn't available yet, but it could be something added at some point if there is enough demand, the counter catalog is broad enough, and the polling frequency often enough.
Cheers,
Chris Madden
Storage Architect, NetApp EMEA (and author of Harvest)
Blog: It all begins with data
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