We have been using Cassandra 0.6 and now have Column Families with millions of keys. We are interested in using the new Secondary Index feature available in the 0.7 but couldn't find any documentation on how the new index is stored. Is there any disk-space limitation or is the index stored similar to keys in that it's spread over multiple nodes? I've tried combing through the Cassandra site for an answer but to no avail.