Hi Jan,
You can take a look at the template file, which lists the objects and counters that are collected by Harvest. E.g. open template/default/cdot-9.6.0.conf (or replace "9.6.0" with the version that most closely matches to your cDot).
Next, you can use the utility util/perf-counters-utility to get info of about the counters. E.g. to see the counters of object volume, run:
/util/perf-counters-utility -host HOST -user USER -pass PASS -f volume -c
(replace HOST, USER, PASS with the hostname, usename and password of your Cdot system).
You can also use this utility to explore objects / counters that are not collected by Harvest, add them to the template to make Harvest collect them.
Let me know if you need more help.