Veritas Storage Foundation 5.0 for Oracle RAC Configuration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Introducing Serviceguard Extension for RAC
Cluster Interconnect Communication Channel
Chapter 1
16
Cluster Interconnect Communication Channel
The cluster interconnect provides the communication channel for all system-to-system
communication, in addition to one-node communication between modules. Low Latency
Transport (LLT) and Group Membership Services/Atomic Broadcast (GAB) make up the
SG SMS Serviceguard for Oracle RAC communications package central to the operation
of SGeRAC.
Refer to Using Serviceguard Extension for RAC for additional information.
Low Latency Transport
LLT provides fast, kernel-to-kernel communications and monitors network connections.
LLT functions as a high performance replacement for the IP stack and runs directly on
top of the Data Link Protocol Interface (DLPI) layer. The use of LLT rather than IP
removes latency and overhead associated with the IP stack. The major functions of LLT
are traffic distribution, heartbeats, and support for RAC Inter-Process Communications
(VCSIPC).
• Traffic Distribution
LLT distributes (load-balances) internode communication across all available cluster
interconnect links. All cluster communications are evenly distributed across as many
as eight network links for performance and fault resilience. If a link fails, LLT
redirects traffic to the remaining links.
• Heartbeats
LLT is responsible for sending and receiving heartbeat traffic over network links.
The Group Membership Services function of GAB uses heartbeats to determine
cluster membership.
• VCSIPC
RAC Inter-Process Communications (VCSIPC) uses the VCSIPC shared library for
these communications. VCSIPC leverages all features of LLT and uses LMX, an LLT
multiplexer, to provide fast data transfer between Oracle processes on different
nodes.
Group Membership Services/Atomic Broadcast
The GAB protocol is responsible for cluster membership and cluster communications.
Figure 1-4 Cluster Communication
GAB Messaging
- Cluster Membership/State
Server
Server
NICNIC
NIC NIC
- Datafile Management
- File System Metadata
- Volume Management