HP XC System Software Administration Guide Version 3.1

1.6.2 Software Distribution
The HP XC system uses the SystemImager tool to synchronize the configuration of nodes across the cluster
using image propagation. This simplifies installation of the initial software and upgrading software and
configuration files. For more information, see Chapter 10: Distributing Software Throughout the System
(page 129).
1.7 Improved Availability
The HP XC system offers improved availability, which enables the HP XC System Software to interact
with optional Availability tools, such as HP Serviceguard. These tools are optional: you must order them
from the manufacturer and install them according to the manufacturer's prescribed installation procedure.
The availability tools are located in a directory that the manufacturer chooses.
Improved availability provides for the failover of configured services from a failed node to another
configured in the HP XC system.
For more information on improved availability, see Chapter 2 (page 43).
1.8 Networking
The HP XC system relies on networking services to communicate among its nodes. It uses the Linux Virtual
Server, Network Time Protocol, Network Address Translation, and Network Information Service.
1.8.1 Linux Virtual Server for HP XC Cluster Alias
The HP XC system uses the Linux Virtual Server (LVS) to present a single host name for user logins. LVS
is a highly scalable virtual server built on a cluster of real servers. By using LVS, the architecture of the
HP XC system is transparent to end users, and they see only a single virtual server. This eliminates the
need for users to know how the cluster is configured in order to successfully log in and use it. Any changes
in the system configuration are transparent to end users. LVS also provides load balancing across login
nodes, which distributes login requests to different servers.
Figure 1-3 illustrates the use of LVS in an HP XC system.
Figure 1-3 LVS View of Cluster
1.8.2 Network Time Protocol
One node in an HP XC system acts as the internal Network Time Protocol (NTP) server for all the other
nodes. By default this is the head node. All other nodes are NTP clients of this server.
You can specify where the internal NTP server gets the time. You can specify up to four external time
sources if the internal server has a connection to an outside network. You can also choose to use the internal
server's own clock as the time source.
38 HP XC Administration Environment