Symantec 5 manual About LLT and GAB, About network channels for heartbeating

Introducing Veritas Cluster Server	15
About VCS basics

Figure 1-2 Two examples of shared storage configurations

Fully shared storage

Distributed shared storage

About LLT and GAB

VCS uses two components, LLT and GAB, to share data over private networks among systems. These components provide the performance and reliability that VCS requires.

LLT (Low Latency Transport) provides fast, kernel-to-kernel communications, and monitors network connections.

LLT configuration files are as follows:

■/etc/llthosts—lists all the nodes in the cluster

■/etc/llttab file—describes the local system’s private network links to the other nodes in the cluster

GAB (Group Membership and Atomic Broadcast) provides the global message order that is required to maintain a synchronized state among the nodes. It monitors disk communications such as the VCS heartbeat utility. The /etc/gabtab file is the GAB configuration file.

See “About the LLT and GAB configuration files” on page 105.

About network channels for heartbeating

For the VCS private network, two network channels must be available to carry heartbeat information. These network connections also transmit other VCS-related information.

Each Linux for IBM Power cluster configuration requires at least two network channels between the systems. The requirement for two channels protects your cluster against network partitioning. For more information on network partitioning, refer to the Veritas Cluster Server User's Guide.