The effect of accessing blocks in the global cache and maintaining coherency is represented by:
The Global Cache Service (GCS) statistics for current and cr blocks, for example, gc current blocks received, gc cr blocks received, and so on
The GCS wait events, for gc current block 3-way, gc cr grant 2-way, and so on
The response time for cache fusion transfers is determined by the messaging and processing times imposed by the physical interconnect components, the IPC protocol and the GCS protocol. It is not affected by disk I/O factors other than occasional log writes. The cache fusion protocol does not require I/O to data files to guarantee cache coherency and Oracle RAC inherently does not cause any more I/O to disk than a nonclustered instance.