Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

Figure 1-4
Communication stack
CVM
CFS
ODM
CVM
CFS
ODM
Node 1 Node 2
Oracle
RAC
Oracle
RAC
LLT/
GAB
LLT/
GAB
VCS
Core
VCS
Core
VCS Cluster State
Cache Fusion/Lock
Mgmt
Data File
Management
File System
MetaData
Volume Management
Cluster interconnect communication channel
The cluster interconnect provides an additional communication channel for all
system-to-system communication, separate from the one-node communication
between modules. Low Latency Transport (LLT) and Group Membership
Services/Atomic Broadcast (GAB) make up the VCS communications package
central to the operation of SF Oracle RAC.
In a standard operational state, significant traffic through LLT and GAB results
from Lock Management, while traffic for other data is relatively sparse.
About Low Latency Transport (LLT)
The Low Latency Transport protocol is used for all cluster communications as a
high-performance, low-latency replacement for the IP stack.
LLT has the following two major functions:
■ Traffic distribution
LLT provides the communications backbone for GAB. LLT distributes (load
balances) inter-system communication across all configured network links.
This distribution ensures all cluster communications are evenly distributed
across all network links for performance and fault resilience. If a link fails,
25Overview of Veritas Storage Foundation for Oracle RAC
Component products and processes of SF Oracle RAC