Cassandra 1.1.6 - Disk usage and Load displayed in ring doesn't match

We have 8 node cluster. Replication factor is 3. For some of the nodes the Disk usage (du -ksh .) in the data directory for CF doesn't match the Load reported in nodetool ring command. When we expanded the cluster from 4 node to 8 nodes (4 weeks back), everything was okay. Over period of last 2-3

Conference or training recommendations

I¹d like to attend a conference or some form of training to become more proficient and knowledgable about Cassandra. Any suggestions?