fluentd's greatest advantage is, it's written in Ruby. So, it's really easy to write the plugin for any datastores.

This is HDFS (Hoop, the HDFS REST gateway) plugin.

* https://github.com/tagomoris/fluent-plugin-hoop

And also, Cassandra plugin are now in under development.

* https://github.com/tomitakazutaka/fluent-plugin-cassandra

You can see the user contributed plugin list here.

* https://github.com/tomitakazutaka/fluent-plugin-cassandra