The second phase of SolrCloud has been in full swing for a couple of months now and it looks like we are going to be able to commit this work to trunk very soon! In Phase1 we built on top of Solr’s distributed search capabilities and added cluster state, central config, and built-in read side fault tolerance. Phase 2 is even more ambitious and focuses on the write side. We are talking full-blown fault tolerance for reads and writes, near real-time support, real-time GET, true single node durability, optimistic locking, cluster elasticity, improvements to the Phase 1 features, and more.
Once we get Phase2 into trunk we will work on hardening and finishing a couple missing features – then SolrCloud should be ready to be part of the upcoming Lucene/Solr 4.0 release.
If you want to read more about SolrCloud and where we are with Phase 2, check out the new wiki page that we are working on at http://wiki.apache.org/solr/SolrCloud2 - feedback appreciated!