Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 4.6 Installation guide

Red Hat Cluster Suite Overview
Red Hat Cluster Suite for
Red Hat Enterprise Linux
4.6
4.6
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Red Hat Cluster Suite Overview provides an overview of Red Hat Cluster Suite for Red Hat
Enterprise Linux 4.6.
Red Hat Cluster Suite Overview

Red Hat Cluster Suite Overview: Red Hat Cluster Suite for
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Red Hat Cluster Suite Overview

Introduction ..............................................................................................................vii
1. Document Conventions ................................................................................ viii
2. Feedback ......................................................................................................ix
1. Red Hat Cluster Suite Overview .............................................................................. 1
1. Cluster Basics ................................................................................................ 1
2. Red Hat Cluster Suite Introduction .................................................................. 2
3. Cluster Infrastructure ...................................................................................... 4
3.1. Cluster Management ........................................................................... 5
3.2. Lock Management ............................................................................... 7
3.3. Fencing .............................................................................................. 7
3.4. Cluster Configuration System ..............................................................12
4. High-availability Service Management ............................................................14
5. Red Hat GFS ................................................................................................17
5.1. Superior Performance and Scalability ..................................................19
5.2. Performance, Scalability, Moderate Price .............................................19
5.3. Economy and Performance .................................................................20
6. Cluster Logical Volume Manager ....................................................................21
7. Global Network Block Device .........................................................................25
8. Linux Virtual Server .......................................................................................26
8.1. Two-Tier LVS Topology ......................................................................28
8.2. Three-Tier LVS Topology ....................................................................31
8.3. Routing Methods ................................................................................33
8.4. Persistence and Firewall Marks ...........................................................36
9. Cluster Administration Tools ..........................................................................37
9.1. Conga ...............................................................................................37
9.2. Cluster Administration GUI ..................................................................40
9.3. Command Line Administration Tools ...................................................43
10. Linux Virtual Server Administration GUI ........................................................45
10.1. CONTROL/MONITORING ................................................................45
10.2. GLOBAL SETTINGS ........................................................................47
10.3. REDUNDANCY ................................................................................48
10.4. VIRTUAL SERVERS ........................................................................49
2. Red Hat Cluster Suite Component Summary ..........................................................57
1. Cluster Components .....................................................................................57
2. Man Pages ...................................................................................................63
3. Compatible Hardware ....................................................................................65
Index .......................................................................................................................67
v

vi

Introduction
This document provides a high-level overview of Red Hat Cluster Suite for Red Hat Enterprise
Linux 4.6. Although the information in this document is an overview, you should have advanced
working knowledge of Red Hat Enterprise Linux and understand the concepts of server
computing to gain a good comprehension of the information. For more information about using
Red Hat Enterprise Linux, refer to the following resources:
•Red Hat Enterprise Linux Installation Guide — Provides information regarding installation.
•Red Hat Enterprise Linux Introduction to System Administration — Provides introductory
information for new Red Hat Enterprise Linux system administrators.
•Red Hat Enterprise Linux System Administration Guide — Provides more detailed information
about configuring Red Hat Enterprise Linux to suit your particular needs as a user.
•Red Hat Enterprise Linux Reference Guide — Provides detailed information suited for more
experienced users to reference when needed, as opposed to step-by-step instructions.
•Red Hat Enterprise Linux Security Guide — Details the planning and the tools involved in
creating a secured computing environment for the data center, workplace, and home.
This document contains overview information about Red Hat Cluster Suite for Red Hat
Enterprise Linux 4.6 and is part of a documentation set that provides conceptual, procedural,
and reference information about Red Hat Cluster Suite for Red Hat Enterprise Linux 4.6.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML,
PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online at
http://www.redhat.com/docs/.
For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux 4.6, refer to the
following resources:
•Configuring and Managing a Red Hat Cluster — Provides information about installing,
configuring and managing Red Hat Cluster components.
•LVM Administrator's Guide: Configuration and Administration — Provides a description of the
Logical Volume Manager (LVM), including information on running LVM in a clustered
environment.
•Global File System: Configuration and Administration — Provides information about installing,
configuring, and maintaining Red Hat GFS (Red Hat Global File System).
•Using Device-Mapper Multipath — Provides information about using the Device-Mapper
Multipath feature of Red Hat Enterprise Linux 4.6.
•Using GNBD with Global File System — Provides an overview on using Global Network Block
Device (GNBD) with Red Hat GFS.
vii

•Linux Virtual Server Administration — Provides information on configuring high-performance
systems and services with the Linux Virtual Server (LVS).
•Red Hat Cluster Suite Release Notes — Provides information about the current release of
Red Hat Cluster Suite.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML,
PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online at
http://www.redhat.com/docs/.
1. Document Conventions
Certain words in this manual are represented in different fonts, styles, and weights. This
highlighting indicates that the word is part of a specific category. The categories include the
following:
Courier font
Courier font represents commands,file names and paths, and prompts .
When shown as below, it indicates computer output:
Desktop about.html logs paulwesterberg.png
Mail backupfiles mail reports
bold Courier font
Bold Courier font represents text that you are to type, such as: service jonas start
If you have to run a command as root, the root prompt (#) precedes the command:
#gconftool-2
italic Courier font
Italic Courier font represents a variable, such as an installation directory:
install_dir/bin/
bold font
Bold font represents application programs and text found on a graphical interface.
When shown like this: OK , it indicates a button on a graphical application interface.
Additionally, the manual uses different strategies to draw your attention to pieces of information.
In order of how critical the information is to you, these items are marked as follows:
Introduction
viii

Note
A note is typically information that you need to understand the behavior of the
system.
Tip
A tip is typically an alternative way of performing a task.
Important
Important information is necessary, but possibly unexpected, such as a
configuration change that will not persist after a reboot.
Caution
A caution indicates an act that would violate your support agreement, such as
recompiling the kernel.
Warning
A warning indicates potential data loss, as may happen when tuning hardware
for maximum performance.
2. Feedback
If you spot a typo, or if you have thought of a way to make this document better, we would love
to hear from you. Please submit a report in Bugzilla (http://bugzilla.redhat.com/bugzilla/) against
the component rh-cs.
Be sure to mention the document's identifier:
sac_cl_over(EN)-4.6 (2008-06-01:T23:07)
Feedback
ix

By mentioning this document's identifier, we know exactly which version of the guide you have.
If you have a suggestion for improving the documentation, try to be as specific as possible. If
you have found an error, please include the section number and some of the surrounding text
so we can find it easily.
Introduction
x

Red Hat Cluster Suite Overview
Clustered systems provide reliability, scalability, and availability to critical production services.
Using Red Hat Cluster Suite, you can create a cluster to suit your needs for performance, high
availability, load balancing, scalability, file sharing, and economy. This chapter provides an
overview of Red Hat Cluster Suite components and functions, and consists of the following
sections:
•Section 1, “Cluster Basics”
•Section 2, “Red Hat Cluster Suite Introduction”
•Section 3, “Cluster Infrastructure”
•Section 4, “High-availability Service Management”
•Section 5, “Red Hat GFS”
•Section 6, “Cluster Logical Volume Manager”
•Section 7, “Global Network Block Device”
•Section 8, “Linux Virtual Server”
•Section 9, “Cluster Administration Tools”
•Section 10, “Linux Virtual Server Administration GUI”
1. Cluster Basics
A cluster is two or more computers (called nodes or members) that work together to perform a
task. There are four major types of clusters:
• Storage
• High availability
• Load balancing
• High performance
Storage clusters provide a consistent file system image across servers in a cluster, allowing the
servers to simultaneously read and write to a single shared file system. A storage cluster
simplifies storage administration by limiting the installation and patching of applications to one
file system. Also, with a cluster-wide file system, a storage cluster eliminates the need for
redundant copies of application data and simplifies backup and disaster recovery. Red Hat
Cluster Suite provides storage clustering through Red Hat GFS.
Chapter 1.
1

High-availability clusters provide continuous availability of services by eliminating single points
of failure and by failing over services from one cluster node to another in case a node becomes
inoperative. Typically, services in a high-availability cluster read and write data (via read-write
mounted file systems). Therefore, a high-availability cluster must maintain data integrity as one
cluster node takes over control of a service from another cluster node. Node failures in a
high-availability cluster are not visible from clients outside the cluster. (High-availability clusters
are sometimes referred to as failover clusters.) Red Hat Cluster Suite provides high-availability
clustering through its High-availability Service Management component.
Load-balancing clusters dispatch network service requests to multiple cluster nodes to balance
the request load among the cluster nodes. Load balancing provides cost-effective scalability
because you can match the number of nodes according to load requirements. If a node in a
load-balancing cluster becomes inoperative, the load-balancing software detects the failure and
redirects requests to other cluster nodes. Node failures in a load-balancing cluster are not
visible from clients outside the cluster. Red Hat Cluster Suite provides load-balancing through
LVS (Linux Virtual Server).
High-performance clusters use cluster nodes to perform concurrent calculations. A
high-performance cluster allows applications to work in parallel, therefore enhancing the
performance of the applications. (High performance clusters are also referred to as
computational clusters or grid computing.)
Note
The cluster types summarized in the preceding text reflect basic configurations;
your needs might require a combination of the clusters described.
2. Red Hat Cluster Suite Introduction
Red Hat Cluster Suite (RHCS) is an integrated set of software components that can be
deployed in a variety of configurations to suit your needs for performance, high-availability, load
balancing, scalability, file sharing, and economy.
RHCS consists of the following major components (refer to Figure 1.1, “Red Hat Cluster Suite
Introduction”):
• Cluster infrastructure — Provides fundamental functions for nodes to work together as a
cluster: configuration-file management, membership management, lock management, and
fencing.
• High-availability Service Management — Provides failover of services from one cluster node
to another in case a node becomes inoperative.
• Cluster administration tools — Configuration and management tools for setting up,
configuring, and managing a Red Hat cluster. The tools are for use with the Cluster
Chapter 1. Red Hat Cluster Suite Overview
2

Infrastructure components, the High-availability and Service Management components, and
storage.
• Linux Virtual Server (LVS) — Routing software that provides IP-Load-balancing. LVS runs in
a pair of redundant servers that distributes client requests evenly to real servers that are
behind the LVS servers.
You can supplement Red Hat Cluster Suite with the following components, which are part of an
optional package (and not part of Red Hat Cluster Suite):
• Red Hat GFS (Global File System) — Provides a cluster file system for use with Red Hat
Cluster Suite. GFS allows multiple nodes to share storage at a block level as if the storage
were connected locally to each cluster node.
• Cluster Logical Volume Manager (CLVM) — Provides volume management of cluster storage.
Note
When you create or modify a CLVM volume for a clustered environment, you
must ensure that you are running the clvmd daemon. For further information,
refer to Section 6, “Cluster Logical Volume Manager”.
• Global Network Block Device (GNBD) — An ancillary component of GFS that exports
block-level storage to Ethernet. This is an economical way to make block-level storage
available to Red Hat GFS.
For a lower level summary of Red Hat Cluster Suite components and optional software, refer to
Chapter 2, Red Hat Cluster Suite Component Summary.
Red Hat Cluster Suite Introduction
3

Figure 1.1. Red Hat Cluster Suite Introduction
Note
Figure 1.1, “Red Hat Cluster Suite Introduction” includes GFS, CLVM, and
GNBD, which are components that are part of an optional package and not part
of Red Hat Cluster Suite.
3. Cluster Infrastructure
The Red Hat Cluster Suite cluster infrastructure provides the basic functions for a group of
computers (called nodes or members) to work together as a cluster. Once a cluster is formed
using the cluster infrastructure, you can use other Red Hat Cluster Suite components to suit
your clustering needs (for example, setting up a cluster for sharing files on a GFS file system or
setting up service failover). The cluster infrastructure performs the following functions:
• Cluster management
• Lock management
Chapter 1. Red Hat Cluster Suite Overview
4

• Fencing
• Cluster configuration management
3.1. Cluster Management
Cluster management manages cluster quorum and cluster membership. One of the following
Red Hat Cluster Suite components performs cluster management: CMAN (an abbreviation for
cluster manager) or GULM (Grand Unified Lock Manager). CMAN operates as the cluster
manager if a cluster is configured to use DLM (Distributed Lock Manager) as the lock manager.
GULM operates as the cluster manager if a cluster is configured to use GULM as the lock
manager. The major difference between the two cluster managers is that CMAN is a distributed
cluster manager and GULM is a client-server cluster manager. CMAN runs in each cluster node;
cluster management is distributed across all nodes in the cluster (refer to Figure 1.2,
“CMAN/DLM Overview”). GULM runs in nodes designated as GULM server nodes; cluster
management is centralized in the nodes designated as GULM server nodes (refer to Figure 1.3,
“GULM Overview”). GULM server nodes manage the cluster through GULM clients in the cluster
nodes. With GULM, cluster management operates in a limited number of nodes: either one,
three, or five nodes configured as GULM servers.
The cluster manager keeps track of cluster quorum by monitoring the count of cluster nodes that
run cluster manager. (In a CMAN cluster, all cluster nodes run cluster manager; in a GULM
cluster only the GULM servers run cluster manager.) If more than half the nodes that run cluster
manager are active, the cluster has quorum. If half the nodes that run cluster manager (or
fewer) are active, the cluster does not have quorum, and all cluster activity is stopped. Cluster
quorum prevents the occurrence of a "split-brain" condition — a condition where two instances
of the same cluster are running. A split-brain condition would allow each cluster instance to
access cluster resources without knowledge of the other cluster instance, resulting in corrupted
cluster integrity.
In a CMAN cluster, quorum is determined by communication of heartbeats among cluster nodes
via Ethernet. Optionally, quorum can be determined by a combination of communicating
heartbeats via Ethernet and through a quorum disk. For quorum via Ethernet, quorum consists
of 50 percent of the node votes plus 1. For quorum via quorum disk, quorum consists of
user-specified conditions.
Note
In a CMAN cluster, by default each node has one quorum vote for establishing
quorum. Optionally, you can configure each node to have more than one vote.
In a GULM cluster, the quorum consists of a majority of nodes designated as GULM servers
according to the number of GULM servers configured:
Cluster Management
5

• Configured with one GULM server — Quorum equals one GULM server.
• Configured with three GULM servers — Quorum equals two GULM servers.
• Configured with five GULM servers — Quorum equals three GULM servers.
The cluster manager keeps track of membership by monitoring heartbeat messages from other
cluster nodes. When cluster membership changes, the cluster manager notifies the other
infrastructure components, which then take appropriate action. For example, if node A joins a
cluster and mounts a GFS file system that nodes B and C have already mounted, then an
additional journal and lock management is required for node A to use that GFS file system. If a
cluster node does not transmit a heartbeat message within a prescribed amount of time, the
cluster manager removes the node from the cluster and communicates to other cluster
infrastructure components that the node is not a member. Again, other cluster infrastructure
components determine what actions to take upon notification that node is no longer a cluster
member. For example, Fencing would fence the node that is no longer a member.
Figure 1.2. CMAN/DLM Overview
Chapter 1. Red Hat Cluster Suite Overview
6

Figure 1.3. GULM Overview
3.2. Lock Management
Lock management is a common cluster-infrastructure service that provides a mechanism for
other cluster infrastructure components to synchronize their access to shared resources. In a
Red Hat cluster, one of the following Red Hat Cluster Suite components operates as the lock
manager: DLM (Distributed Lock Manager) or GULM (Grand Unified Lock Manager). The major
difference between the two lock managers is that DLM is a distributed lock manager and GULM
is a client-server lock manager. DLM runs in each cluster node; lock management is distributed
across all nodes in the cluster (refer to Figure 1.2, “CMAN/DLM Overview”). DLM can be the
lock manager only in a cluster configured with CMAN as its cluster manager. GULM runs in
nodes designated as GULM server nodes; lock management is centralized in the nodes
designated as GULM server nodes. GULM server nodes manage locks through GULM clients in
the cluster nodes (refer to Figure 1.3, “GULM Overview”). With GULM, lock management
operates in a limited number of nodes: either one, three, or five nodes configured as GULM
servers. GFS and CLVM use locks from the lock manager. GFS uses locks from the lock
manager to synchronize access to file system metadata (on shared storage). CLVM uses locks
from the lock manager to synchronize updates to LVM volumes and volume groups (also on
shared storage).
3.3. Fencing
Fencing is the disconnection of a node from the cluster's shared storage. Fencing cuts off I/O
from shared storage, thus ensuring data integrity.
The cluster infrastructure performs fencing through one of the following programs according to
the type of cluster manager and lock manager that is configured:
Lock Management
7

• Configured with CMAN/DLM — fenced, the fence daemon, performs fencing.
• Configured with GULM servers — GULM performs fencing.
When the cluster manager determines that a node has failed, it communicates to other
cluster-infrastructure components that the node has failed. The fencing program (either fenced
or GULM), when notified of the failure, fences the failed node. Other cluster-infrastructure
components determine what actions to take — that is, they perform any recovery that needs to
done. For example, DLM and GFS (in a cluster configured with CMAN/DLM), when notified of a
node failure, suspend activity until they detect that the fencing program has completed fencing
the failed node. Upon confirmation that the failed node is fenced, DLM and GFS perform
recovery. DLM releases locks of the failed node; GFS recovers the journal of the failed node.
The fencing program determines from the cluster configuration file which fencing method to use.
Two key elements in the cluster configuration file define a fencing method: fencing agent and
fencing device. The fencing program makes a call to a fencing agent specified in the cluster
configuration file. The fencing agent, in turn, fences the node via a fencing device. When
fencing is complete, the fencing program notifies the cluster manager.
Red Hat Cluster Suite provides a variety of fencing methods:
• Power fencing — A fencing method that uses a power controller to power off an inoperable
node
• Fibre Channel switch fencing — A fencing method that disables the Fibre Channel port that
connects storage to an inoperable node
• GNBD fencing — A fencing method that disables an inoperable node's access to a GNBD
server
• Other fencing — Several other fencing methods that disable I/O or power of an inoperable
node, including IBM Bladecenters, PAP, DRAC/MC, HP ILO, IPMI, IBM RSA II, and others
Figure 1.4, “Power Fencing Example” shows an example of power fencing. In the example, the
fencing program in node A causes the power controller to power off node D. Figure 1.5, “Fibre
Channel Switch Fencing Example” shows an example of Fibre Channel switch fencing. In the
example, the fencing program in node A causes the Fibre Channel switch to disable the port for
node D, disconnecting node D from storage.
Chapter 1. Red Hat Cluster Suite Overview
8

Figure 1.4. Power Fencing Example
Fencing
9

Figure 1.5. Fibre Channel Switch Fencing Example
Specifying a fencing method consists of editing a cluster configuration file to assign a
fencing-method name, the fencing agent, and the fencing device for each node in the cluster.
Note
Other fencing parameters may be necessary depending on the type of cluster
manager (either CMAN or GULM) selected in a cluster.
The way in which a fencing method is specified depends on if a node has either dual power
supplies or multiple paths to storage. If a node has dual power supplies, then the fencing
method for the node must specify at least two fencing devices — one fencing device for each
power supply (refer to Figure 1.6, “Fencing a Node with Dual Power Supplies”). Similarly, if a
node has multiple paths to Fibre Channel storage, then the fencing method for the node must
specify one fencing device for each path to Fibre Channel storage. For example, if a node has
two paths to Fibre Channel storage, the fencing method should specify two fencing devices —
one for each path to Fibre Channel storage (refer to Figure 1.7, “Fencing a Node with Dual Fibre
Chapter 1. Red Hat Cluster Suite Overview
10