used to joke about "single node RAC" but now it actually exists!
Basically, One Node is running a RAC database on a single server, rather than across a cluster of servers. There is an Oracle white paper on the topic. Find it here. The money quote is:
"Oracle RAC One Node enables:
• Better server consolidation
• Enhanced protection from failures
• Greater flexibility and workload management
• Better online maintenance
In addition it allows customers to virtualize database storage, standardize their database environment, and, should the need arise, upgrade to a full multi-node Oracle RAC database without downtime or disruption."
