从官方文档中可以看到对Leaf节点的说明：
12c R1官方文档说明：
Leaf Nodes are different from standard Oracle Grid Infrastructure nodes, in that they do not require direct access to shared storage, but instead request data through Hub Nodes. Hub Nodes can run in an Oracle Flex Cluster configuration without having any Leaf Nodes as cluster member nodes, but Leaf Nodes must be members of a cluster that includes at least one Hub Node.
12c R2官方文档说明：
Leaf Nodes are different from standard Oracle Grid Infrastructure nodes, in that they do not require direct access to shared storage, but instead request data through Hub Nodes. Use Leaf Nodes to host read-only database instances.
误解：Leaf节点是可以运行ASM和数据库实例的。
这里在我做12c R1实验时发现，当我将Hub节点转换为Leaf节点时候，ASM实例和数据库实例就会被自动关闭。
很诧异，以为自己哪里搞错了。就网上搜了搜：http://m.blog.csdn.net/u011478909/article/details/76214921这篇博客说明12C R1的leaf节点确实无法运行数据库实例的。不放心，翻墙搜：http://www.orafaq.com/node/2857这篇博客对这个问题进行了说明，由于官方文档没有进行明确的说明，导致了一个已经出版的书也进行了错误的介绍：认为leaf节点可以可以运行数据库实例。
在12c R2中 Leaf节点可以运行只读数据库实例。
参考文档：http://allthingsoracle.com/oracle-flex-cluster-leaf-node-failover/