Pinning a node permanently associates the node name with the node number. If you don't pin them and an instance is down for a long time (past the lease period), the not number can be reused for a different node.
A pool in RAC is a specified group (pool) of server nodes. When you create a policy managed database it is assigned to a pool. RAC instances of that database can be run on one or more nodes within that pool.http://docs.oracle.com/cd/E11882_01/rac ... m#BABBDDGB