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NOTE: CentOS Enterprise Linux is built from the Red Hat Enterprise Linux source code. Other than logo and name changes CentOS Enterprise Linux is compatible with the equivalent Red Hat version. This document applies equally to both Red Hat and CentOS Enterprise Linux.

Chapter 2. Hardware Installation and Operating System Configuration

To set up the hardware configuration and install Red Hat Enterprise Linux, follow these steps:

After setting up the hardware configuration and installing Red Hat Enterprise Linux, install the cluster software.

2.1. Choosing a Hardware Configuration

The Red Hat Cluster Manager allows administrators to use commodity hardware to set up a cluster configuration that meets the performance, availability, and data integrity needs of applications and users. Cluster hardware ranges from low-cost minimum configurations that include only the components required for cluster operation, to high-end configurations that include redundant Ethernet channels, hardware RAID, and power switches.

Regardless of configuration, the use of high-quality hardware in a cluster is recommended, as hardware malfunction is a primary cause of system down time.

Although all cluster configurations provide availability, some configurations protect against every single point of failure. In addition, all cluster configurations provide data integrity, but some configurations protect data under every failure condition. Therefore, administrators must fully understand the needs of their computing environment and also the availability and data integrity features of different hardware configurations to choose the cluster hardware that meets the proper requirements.

When choosing a cluster hardware configuration, consider the following:

Performance requirements of applications and users

Choose a hardware configuration that provides adequate memory, CPU, and I/O resources. Be sure that the configuration chosen can handle any future increases in workload as well.

Cost restrictions

The hardware configuration chosen must meet budget requirements. For example, systems with multiple I/O ports usually cost more than low-end systems with fewer expansion capabilities.

Availability requirements

In a mission-critical production environment, a cluster hardware configuration must protect against all single points of failure, including: disk, storage interconnect, Ethernet channel, and power failure. Environments that can tolerate an interruption in availability (such as development environments) may not require as much protection.

Data integrity under all failure conditions requirement

Using fence devices in a cluster configuration guarantees that service data is protected under every failure condition. These devices enable a node to power cycle another node before restarting its services during failover. Power switches protect against data corruption if an unresponsive (or hanging) node becomes responsive after its services have failed over and then issues I/O to a disk that is also receiving I/O from the other node.

If you are not using power switches in the cluster, cluster service failures can result in services being run on more than one node, which can cause data corruption. Refer to Section 2.5.2 Configuring a Fence Device for more information about the benefits of using power switches in a cluster. It is required that production environments use power switches in the cluster hardware configuration.

2.1.1. Minimum Hardware Requirements

A minimum hardware configuration includes only the hardware components that are required for cluster operation, as follows:

  • At least two servers to run cluster services

  • Ethernet connection for sending heartbeat pings and for client network access

  • Network Switch to connect cluster nodes and resources

  • A fence device

The hardware components described in Table 2-1 can be used to set up a minimum cluster configuration. This configuration does not guarantee data integrity under all failure conditions, because it does not include power switches. Note that this is a sample configuration; it is possible to set up a minimum configuration using other hardware.

Warning Warning

The minimum cluster configuration is not a supported solution and should not be used in a production environment, as it does not guarantee data integrity under all failure conditions.

Hardware Description
At least two server systems Each system becomes a node exclusively for use in the cluster; system hardware requirements are similar to that of Red Hat Enterprise Linux 4.
One network interfaces for each node One network interface connects to a hub or switch for cluster connectivity.
One network cable with RJ45 connectors Network cables connect to the network interface on each node for client access and heartbeat packets.
RAID storage enclosure The RAID storage enclosure contains one controller with at least two host ports.
Two HD68 SCSI cables Each cable connects one host bus adapter to one port on the RAID controller, creating two single-initiator SCSI buses.

Table 2-1. Example of Minimum Cluster Configuration

The minimum hardware configuration is a cost-effective cluster configuration for development purposes; however, it contains components that can cause service outages if failed. For example, if the RAID controller fails, then all cluster services become unavailable.

To improve availability, protect against component failure, and guarantee data integrity under all failure conditions, the minimum configuration is shown in Table 2-2.

Problem Solution
Disk failure Hardware RAID to replicate data across multiple disks
RAID controller failure Dual RAID controllers to provide redundant access to disk data
Network interface failure Ethernet channel bonding and failover
Power source failure Redundant uninterruptible power supply (UPS) systems
Machine failure Power switches

Table 2-2. Improving Availability and Data Integrity

Figure 2-1 illustrates a hardware configuration with improved availability. This configuration uses a fence device (in this case, a network-attached power switch) and the nodes are configured for Red Hat GFS storage attached to a Fibre Channel SAN switch. For more information about configuring and using Red Hat GFS, refer to the Red Hat GFS Administrator's Guide.

Figure 2-1. Hardware Configuration for Improved availability

A hardware configuration that guarantees data integrity under failure conditions can include the following components:

  • At least two servers to run cluster services

  • Switched Ethernet connection between each node for heartbeat pings and for client network access

  • Dual-controller RAID array or redundant access to SAN or other storage for shared partitions and service data

  • Power switches to enable each node to power-cycle the other nodes during the failover process

  • Ethernet interfaces configured to use channel bonding

  • At least two UPS systems for a highly-available source of power

The components described in Table 2-3 can be used to set up a no single point of failure cluster configuration that includes two single-initiator SCSI buses and power switches to guarantee data integrity under all failure conditions. Note that this is a sample configuration; it is possible to set up a no single point of failure configuration using other hardware.

Hardware Description
Two servers (up to 16 supported)
Each node includes the following hardware:
Two network interfaces for:
Client network access
Fence device connection
One network switch A network switch enables the connection of multiple nodes to a network.
Three network cables (each node) Two cables to connect each node to the redundant network switches and a cable to connect to the fence device.
Two RJ45 to DB9 crossover cables RJ45 to DB9 crossover cables connect a serial port on each node to the Cyclades terminal server.
Two power switches Power switches enable each node to power-cycle the other node before restarting its services. Two RJ45 Ethernet cables for a node are connected to each switch.
FlashDisk RAID Disk Array with dual controllers Dual RAID controllers protect against disk and controller failure. The RAID controllers provide simultaneous access to all the logical units on the host ports.
Two HD68 SCSI cables HD68 cables connect each host bus adapter to a RAID enclosure "in" port, creating two single-initiator SCSI buses.
Two terminators Terminators connected to each "out" port on the RAID enclosure terminate both single-initiator SCSI buses.
Redundant UPS Systems UPS systems provide a highly-available source of power. The power cables for the power switches and the RAID enclosure are connected to two UPS systems.

Table 2-3. Example of a No Single Point of Failure Configuration

Cluster hardware configurations can also include other optional hardware components that are common in a computing environment. For example, a cluster can include a network switch or network hub, which enables the connection of the nodes to a network. A cluster may also include a console switch, which facilitates the management of multiple nodes and eliminates the need for separate monitors, mouses, and keyboards for each node.

One type of console switch is a terminal server, which enables connection to serial consoles and management of many nodes from one remote location. As a low-cost alternative, you can use a KVM (keyboard, video, and mouse) switch, which enables multiple nodes to share one keyboard, monitor, and mouse. A KVM is suitable for configurations in which access to a graphical user interface (GUI) to perform system management tasks is preferred.

When choosing a system, be sure that it provides the required PCI slots, network slots, and serial ports. For example, a no single point of failure configuration requires multiple bonded Ethernet ports. Refer to Section 2.3.1 Installing the Basic Cluster Hardware for more information.

2.1.2. Choosing the Type of Fence Device

The Red Hat Cluster Manager implementation consists of a generic power management layer and a set of device-specific modules which accommodate a range of power management types. When selecting the appropriate type of fence device to deploy in the cluster, it is important to recognize the implications of specific device types.

Important Important

Use of a fencing method is an integral part of a production cluster environment. Configuration of a cluster without a fence device is not supported.

Red Hat Cluster Manager supports several types of fencing methods, including network power switches, fabric switches, and Integrated Power Management hardware. Table 2-5 summarizes the supported types of fence devices and some examples of brands and models that have been tested with Red Hat Cluster Manager.

Ultimately, choosing the right type of fence device to deploy in a cluster environment depends on the data integrity requirements versus the cost and availability of external power switches.

  Published under the terms of the GNU General Public License Design by Interspire