WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

7.5.2 Hardware high availability
Although modern hardware is reliable and many components are fault tolerant,
hardware can fail. Any mechanical component has an expected failure rate and a
projected useful life until failure.
To mitigate power failures, you can configure the equipment to have dual power
supplies. With a dual power supply configuration, you can further mitigate power
failures by plugging each power supply into separate circuits in the data center.
For servers, using multiple network interface cards in an adapter teaming
configuration allows a server to bind one IP address to more than one adapter,
and then provide failover facilities for the adapter. This, of course, should be
extended by plugging each adapter into separate switches as well to mitigate the
failure of a switch within the network infrastructure.
Hardware availability for servers at the disk level is also an important
consideration. External disk drive arrays and hard disk drive racks can be
deployed to provide redundant paths to the data, as well as make the disks
available independent of server failure. When working with disks, consider the
appropriate redundant array of inexpensive disks (RAID) levels for your disks.
Network hardware availability can be addressed by most major vendors. There is
now built-in support for stateful failover of firewalls, trunking of switches, and
failover for routers. These devices also support duplicate power supplies, multiple
controllers, and management devices.
7.5.3 Process high availability
In WebSphere Application Server, the concept of a singleton process is used.
Although not a new concept in WebSphere Application Server V7.0, it is
important to understand what this represents in the environment.
A singleton process is an executing function that can exist in only one location at
any given instance, or multiple instances of this function operate independently of
one another. In any system, there are likely to be singleton processes that are
key components of the system functionality.
WebSphere Application Server uses a high availability manager to provide
availability for singleton processes. We discuss this further in 7.5.7, “WebSphere
Application Server high availability features” on page 250,
Chapter 7. Performance, scalability, and high availability 247