NIO support in the latest Solr development versions does not work yet (I previously advised that some people with possible lock contention problems try it out). We'll let you know when it's fixed, but in the meantime you can always set the system property "org.apache.lucene.FSDirectory.class" to "org.apache.lucene.store.NIOFSDirectory" to try it out.
for example: java -Dorg.apache.lucene.FSDirectory.class=org.apache.lucene.store.NIOFSDirectory -jar start.jar -Yonik
