Make sure stats are enabled for riak (riak_kv_stat=true)
Add something like this to your SD config:
[Riak]
stats_url: http://127.0.0.1:8098/stats
You can also add a comma-separated list of stats to include or exclude with whitelist or blacklist, respectively.
You can run curl 10.0.0.2:8098/stats | python -m json.tool to get an
idea of what stats are available.