fill in missing bits from wikidot carbon page

docs/carbon-daemons.rst

@@ -3,20 +3,23 @@ The Carbon Daemons
 
 When we talk about "Carbon" we mean one or more of various daemons that make up the
 storage backend of a Graphite installation. In simple installations, there is typically
-only one daemon, ``carbon-cache.py``. This document gives a brief overview of what
-each daemon does and how you can use them to build a more sophisticated storage backend.
+only one daemon, ``carbon-cache.py``. As an installation grows, the ``carbon-relay.py``
+and ``carbon-aggregator.py`` daemons can be introduced to distribute metrics load and
+perform custom aggregations, respectively.
 
 All of the carbon daemons listen for time-series data and can accept it over a common
 set of :doc:`protocols </feeding-carbon>`. However, they differ in what they do with
-the data once they receive it.
+the data once they receive it. This document gives a brief overview of what each daemon
+does and how you can use them to build a more sophisticated storage backend.
 
 
 carbon-cache.py
 ---------------
 
 ``carbon-cache.py`` accepts metrics over various protocols and writes them to disk as efficiently as
-possible. This requires caching metric values in RAM as they are received, and
-flushing them to disk on an interval using the underlying `whisper` library.
+possible. This requires caching metric values in RAM as they are received, and flushing them to disk
+on an interval using the underlying `whisper` library. It also provides a query service for in-memory
+metric datapoints, used by the Graphite webapp to retrieve "hot data".
 
 ``carbon-cache.py`` requires some basic configuration files to run: