Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 6 - Install, Configure and Database Creation

Communication Stack

Low Level Transport (LLT)

Group membership services/Atomic Broadcast (GAB).

Veritas has implemented its own communication transport for the node message transfers. It is called Low Latency Transport (LLT). LLT provides kernel-to-kernel communication and monitors network connections. It is a replacement for the IP stack. LLT runs on top of the data link protocol interface (DPLI). The use of LLT rather than IP provides low latency and removes the overhead usually associated with the IP stack. When implemented, RAC IPC uses the VCSIPC shared library for inter-process communication. LLT also distributes inter-node communication across all available private interconnects, which can reach as many as 8. LLT, is also responsible for heartbeat message transfers among the nodes.

GAB is responsible for monitoring the cluster membership. As the nodes or members join and exit, the GAB framework keeps track. Cluster membership is determined by the LLT heartbeats. The GAB component handles the point-to-point message delivery and the broadcast messages for all the nodes. Atomic broadcast ensures that all systems receive all messages.

Shared Storage Configuration

Setting up volumes and making sure the cluster file system is accessible by all nodes configures the shared storage. In sum, the volumes and the CFS depend on the physical storage. The cluster volume manager manages all related objects such as physical disks (LUNS), disk groups, volumes, and file systems. Oracle uses the ODM (Oracle disk manager) interface to communicate with Veritas volumes and CFS files.