In this article, I’ll describe how to devise
an effective plan to address system availability. You must first understand the
entire system, and how each component affects overall system
availability. By then identifying the most critical system components,
you can intelligently set priorities. Remember that no matter how insignificant
a system component may seem, it can have a profound effect on overall system
availability. Once you identify the most critical components, seek ways to
improve their reliability, recoverability, serviceability, and manageability.
To improve system availability, first identify all the
system components that work together to enable a user’s application to run. A
chain is only as strong as its weakest link. If your system has one component
that is prone to failure, your entire system is prone to failure.
Most systems can be divided into the following elements:
- Server – This is the portion of the system where most data is stored
or processed. The server fulfills transaction requests sent to it and
sends the results to the requestor of the transaction. For example, in a
bank Automated Teller Machine (ATM) system, the host is usually the bank
mainframe system, or large server, that manages client bank accounts and
- Client – This is the component
that makes a request from the server. In the ATM example, the client is
the ATM machine.
– This is the component that allows the client to communicate with the
server, and vice versa. In the ATM example, the network is typically a
combination of a private network, the public telephone network, and all
associated communication equipment.
each of these areas, examine all components: hardware, software,
environment, processes and procedures, and personnel.
Hardware is the physical equipment making up the
system. It includes, but is not limited to, the following:
- Central processing unit – The
device that controls the operation of the computer system or other
- Storage devices – Data
repositories, whether permanent or volatile media, such as memory and hard
- Input devices – Components for
receiving commands or data from users or other equipment, for example,
keyboards, mice, and serial ports
- Output devices – Components for
presenting data to the user, such as monitors, speakers, and printers
- Cables – Often neglected but
crucial to the reliability of any computer system
of the programs running in the system that enable it to perform its functions,
- Firmware – This is software
embedded in hardware, acting as the interface between hardware resources
and the operating system. In PCs, this software is also called the Basic
Input/Output System (BIOS).
- Operating system – This is made up
of core programs that allow applications to run on a computer without
directly interfacing with the computer’s hardware components. Common
operating systems include Windows, UNIX, Linux, OS/400 and OS/390.
- Utilities – This software performs
housekeeping and system control functions. Normally, system administrators
or maintenance staffers use these programs.
- Programming software – This software
supports the creation of applications, including languages such as C++,
Java, and COBOL and development tools such as Microsoft Visual Studio.
- Applications – These are programs
designed to perform user-specified tasks or operations. These programs may
be written by the company (in-house applications) or purchased from a
software vendor (off-the-shelf or shrink-wrapped software).
- Middleware – These programs support communication or data exchange
between multiple programs or computer systems.
The Environment covers all the external equipment the
system needs in order to run:
- Power – Including automatic voltage regulators, uninterruptible power
supplies, generators, surge suppressors, and lightning arrestors
- Cooling – Including air conditioning units and dehumidifiers
- Floor space – Including raised flooring and securedaccess areas
Processes and procedures are the operational
activities needed to run the system. These include, but are not limited to:
- Activation – Including power up,
system initialization, application startup, and verification of system
- Operation – Including resource
management, input/output control, job control, and network management
- Systems management – Including
system monitoring and change administration
- Housekeeping – Including backup
and restore, as well as archiving of data
- User management – Including user
and security administration
- Deactivation – Including
application shutdown, system shutdown, and power down
People refers to those who interact with the system:
– Including both internal and external users
support staff – Including operators, system administrators,
programmers, technical support professionals, and others
- Vendors and suppliers – Including
electricity vendors, equipment suppliers, telecommunications providers,
Addressing critical components
After you identify all relevant system components, the next
step is to find the critical system components, those that represent
single points of failure for the system. When these components encounter a
problem, the entire system is affected.
Several approaches are available for reducing the risks
associated with these critical components:
outage frequency – Look for ways to prevent outages from
happening to that critical component, thereby increasing its reliability.
outage duration – If outages cannot be entirely avoided, find
ways to recover immediately from them, thereby improving recoverability.
If recovery is impossible, ensure that the component can be immediately
repaired; in other words, improve serviceability.
outage scope – Minimize the parts of a system that are impacted
by an outage.
- Prevent future outages – Reduce the potential for users
and other external factors to affect system availability, and make it
easier to maintain the system’s health by addressing its manageability.
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