Veritas Storage Foundation™ 5.0.1 for Oracle RAC Installation, Configuration, and Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

Figure 1-3 Communication Stack
RAC
ODM
CFS
CVM
SG/SGeRAC Core
GAB LLT
SGORAC Cluster State
Cache Fusion/Lock Mgmt
Data File Management
File System MetaData
Volume Management
RAC
ODM
CFS
CVM
SG/SGeRAC Core
GAB
LLT
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.
Cluster Interconnect Communication Channel 15