The Group Membership and Atomic Broadcast (GAB) and Low Latency Transport (LLT) are VCS-specific protocols implemented directly on Ethernet data link. They run on redundant data links that connect the nodes in a cluster. VCS requires redundant cluster communication links to avoid single points of failure.

GAB provides membership and messaging for the cluster and its applications. GAB membership also provides orderly startup and shutdown of a cluster. The /etc/gabtab file is used to configure GAB. This file contains the gabconfig command run by GAB on startup. For example, the -n <number> option of the command specifies the number of nodes in the cluster. GAB is configured automatically when you run the SFCFSHA installation script, but you may have to reconfigure GAB when adding nodes to a cluster.

See the gabconfig(1M) manual page.

LLT provides kernel-to-kernel communications and monitors network communications. The LLT/etc/llthosts and /etc/llttab files are configured to set system IDs within a cluster, set cluster IDs for multiple clusters, and tune network parameters such as heartbeat frequency. LLT is implemented so that cluster membership changes are reflected quickly, which in turn enables fast responses.

As with GAB, LLT is configured automatically when you run the VCS installation script. The /etc/llttab and /etc/llthosts files contain information you provide during installation. You may also have to reconfigure LLT when adding nodes to a cluster.

See the llttab(4) and the llthosts(4) manual pages.

See the Veritas Cluster Server Administrator's Guide.

Each component in SFCFSHA registers with a GAB membership port. The port membership identifies nodes that have formed a cluster for the individual components.

Table: Port memberships describes the port memberships.