Administrator's Guide

Cluster File System Architecture
Role of Component Products
Chapter 2
16
Role of Component Products
The HP Serviceguard Storage Management Suite bundles that include CFS also include
the Veritas™ Volume Manager by Symantec (VxVM) and it's cluster component, the
Veritas Storage Foundation™ Cluster Volume Manager by Symantec (CVM). The
following sections introduce cluster communication, membership ports, and CVM
functionality.
Cluster Communication
Group Membership Atomic Broadcast (GAB) and Low Latency Transport (LLT) are
protocols implemented directly on an ethernet data link. They run on redundant data
links that connect the nodes in a cluster. Serviceguard and CFS are in most respects, two
separate clusters. GAB provides membership and messaging for the clusters and their
applications. GAB membership also provides orderly startup and shutdown of clusters.
LLT is the cluster communication transport. The /etc/gabtab file is used to configure
GAB and the /etc/llttab
file is used to configure LLT. Serviceguard cmapplyconf
creates these configuration files each time the CFS package is started and modifies them
whenever you apply changes to the Serviceguard cluster configuration - this keeps the
Serviceguard cluster synchronized with the CFS cluster.
Any attempt to directly modify /etc/gabtab and /etc/llttab will be overwritten by
cmapplyconf (or cmdeleteconf).
Membership Ports
Each component in a CFS 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 f Cluster File system membership
port u Temporarily used by CVM
port v Cluster Volume Manager membership
port w Cluster Volume Manager daemons on different nodes communicate
with one another using this port.
Port memberships are configured automatically and cannot be changed. To display port
memberships, enter the gabconfig -a command.
Veritas™ Cluster Volume Manager Functionality
A VxVM cluster is comprised of nodes sharing a set of devices. The nodes are connected
across a network. CVM (the VxVM cluster component) presents a consistent logical view
of device configurations (including changes) on all nodes. CVM functionality makes
logical volumes and raw device applications accessible throughout a cluster. CVM
enables multiple hosts to concurrently access the logical volumes under its control. If one
node fails, the other nodes can still access the devices. You configure CVM shared storage
after the HP Serviceguard high availability (HA) cluster is configured and running.