Veritas Storage Foundation 5.0.1 Cluster File System Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

2 Cluster File System Architecture
This chapter includes the following topics:
• “Role of Component Products” (page 15)
• “About CFS” (page 16)
• “About Veritas Cluster Volume Manager Functionality” (page 19)
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 ethernet data links. 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 and /etc/llthosts files are
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, /etc/llttab, or /etc/llthosts will be
overwritten by cmapplyconf(or cmdeleteconf).
Membership Ports
Each component in a CFS registers with a GAB 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.
Role of Component Products 15