IBM AIX Continuous Availability Features - IBM Redbooks

1.6.2 Availability
1.6.3 Serviceability
For all operating system or application errors, recovery must be attempted. When an error
occurs, it is not valid to simply give up and terminate processing. Instead, the operating
system or application must at least try to keep the component affected by the error up and
running. If that is not possible, the operating system or application should make every effort to
capture the error data and automate system restart as quickly as possible.
The amount of effort put into the recovery should, of course, be proportional to the impact of a
failure and the reasonableness of “trying again”. If actual recovery is not feasible, then the
impact of the error should be reduced to the minimum appropriate level.
Today, many customers require that recovery processing be subject to a time limit and have
concluded that rapid termination with quick restart or takeover by another application or
system is preferable to delayed success. However, takeover strategies rely on redundancy
that becomes more and more expensive as systems get larger, and in most cases the main
reason for quick termination is to begin a lengthy takeover process as soon as possible.
Thus, the focus is now shifting back towards core reliability, and that means quality and
recovery features.
Today’s systems have hot plug capabilities for many subcomponents, from processors to
input/output cards to memory. Also, clustering techniques, reconfigurable input/output data
paths, mirrored disks, and hot swappable hardware should help to achieve a significant level
of system availability.
From a software perspective, availability is the capability of a program to perform its function
whenever it is needed. Availability is a basic customer requirement. Customers require a
stable degree of certainty, and also require that schedules and user needs are met.
Availability gauges the percentage of time a system or program can be used by the customer
for productive use. Availability is determined by the number of interruptions and the duration
of the interruptions, and depends on characteristics and capabilities which include:
► The ability to change program or operating system parameters without rebuilding the
kernel and restarting the system
► The ability to configure new devices without restarting the system
► The ability to install new software or update existing software without restarting the system
► The ability to monitor system resources and programs and cleanup or recover resources
when failures occur
► The ability to maintain data integrity in spite of errors
The AIX operating system includes many availability characteristics and capabilities from
which your overall environment will benefit.
Focus on serviceability is shifting from providing customer support remotely through
conventional methods, such as phone and e-mail, to automated system problem reporting
and correction, without user (or system administrator) intervention.
Hot swapping capabilities of some hardware components enhances the serviceability aspect.
A service processor with advanced diagnostic and administrative tools further enhances the
system serviceability. A System p server's service processor can call home in the service
report, providing detailed information for IBM service to act upon. This automation not only
6 IBM AIX Continuous Availability Features