The Group Membership and Atomic Broadcast (GAB) and Low Latency Transport (LLT) are VCS-specific protocols implemented directly on an 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 file
/etc/gabtab is used to configure GAB. Configuration is done with the
gabconfig command. For example, the
-n option of the command specifies the number of nodes in the cluster. GAB is configured automatically when you run the VCS installation script, but you may have to reconfigure GAB when adding nodes to a cluster.
gabconfig(1m) manual page.
LLT provides kernel-to-kernel communications and monitors network communications. The LLT files
/etc/llttab 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 events such as state 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 file
/etc/llttab contains information you provide during installation. You may also have to reconfigure LLT when adding nodes to a cluster.
llttab(4) manual page.
See the Veritas Cluster Server User's Guide.
Each component in SFCFS registers with a membership port. The port membership identifies nodes that have formed a cluster for the individual components.
Examples of port memberships include the following: