Installation guide

14 Chapter 2:Hardware Installation and Operating System Configuration
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 less expansion capabilities.
Availability requirements
If a computing environment requires the highest degree of availability, such as a production en-
vironment, then a cluster hardware configuration that protects against all single points of failure,
including disk, storage interconnect, heartbeat channel, and power failures is recommended. En-
vironments that can tolerate an interruption in availability, such as development environments,
may not require as much protection. See Section 2.4.1, Configuring Heartbeat Channels, Sec-
tion 2.4.3, Configuring UPS Systems, and Section 2.4.4, Configuring Shared Disk Storage for
more information about using redundant hardware for high availability.
Data integrity under all failure conditions requirement
Using power switches in a cluster configuration guarantees that service data is protected under
every failure condition. These devices enable a cluster system to power cycle the other cluster
system before restarting its services during failover. Power switches protect against data cor-
ruption if an unresponsive (or hanging) system 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 cluster system.
In addition, if a quorum daemon fails on a cluster system, the system is no longer able to monitor
the quorum partitions. If you are not using power switches in the cluster, this error condition may
result in services being run on more than one cluster system, which can cause data corruption.
See Section 2.4.2, Configuring Power Switches for more information about the benefits of using
powerswitches in a cluster. It is recommended that production environments use power switches
or watchdog timers in the cluster configuration.
2.1.1 Shared Storage Requirements
The operation of the cluster depends on reliable, coordinated access to shared storage. In the event of
hardware failure, it is desirable to be able to disconnect one member from the shared storage for repair
without disrupting the other member. Shared storage is truly vital to the cluster configuration.
Testing has shown that it is difficult, if not impossible, to configure reliable multi-initiator parallel
SCSI configurations at data rates above 80 MBytes/sec. using standard SCSI adapters. Further tests
have shown that these configurations can not support online repair because the bus does not work
reliably when the HBA terminators are disabled, and external terminators are used. For these reasons,
multi-initiator SCSI configurations using standard adapters are not supported. Single-initiator parallel
SCSI buses, connected to multi-ported storage devices, or Fibre Channel, are required.
The Red Hat Cluster Manager requires that both cluster members have simultaneous access to the
shared storage. Certain host RAID adapters are capable of providing this type of access to shared