The Role of Component Products

SFCFS includes VERITAS Cluster Server (VCS) and VERITAS Volume Manager (VxVM). The VERITAS Cluster Server (VCS) provides the communication, configuration, and membership services required to create a cluster. VCS is the first component installed and configured to set up a cluster file system.

VCS

GAB and 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. See the gabconfig(1m) manual page for additional information.

LLT provides kernel-to-kernel communications and monitors network communications. The LLT files /etc/llthosts and /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. See the llttab(4) manual page for details on how to modify the LLT configuration. For more information on GAB or LLT, 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:

port a   heartbeat membership

port b   I/O fencing membership

port f   Cluster File system membership

port u   Temporarily used by CVM

port v   Cluster Volume Manager membership

CVM

The VERITAS Volume Manager cluster functionality (CVM) makes logical volumes accessible throughout a cluster. CVM enables multiple hosts to concurrently access the logical volumes under its control. A VxVM cluster comprises nodes sharing a set of devices. The nodes are connected across a network. If one node fails, other nodes can access the devices. The VxVM cluster feature presents the same logical view of the device configurations, including changes, on all nodes. You configure CVM shared storage after VCS sets up a cluster configuration.