IBM AIX Continuous Availability Features - IBM Redbooks

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2.3.15 Concurrent AIX Update
Historically, servicing defects in the kernel has required some sort of interruption to system
services in order to correct the problem. Typically, the interruption is in the form of a system
reboot. This results in significant disruption to production systems, and has numerous
implications to customers, including:
► The temporary loss of system availability and services
► An increased load on other systems
► A possible requirement of an unplanned maintenance window
► Monetary costs resulting from the loss of system availability
In addition, in some situations a diagnostic kernel is produced in order to analyze a problem,
and multiple reboots become necessary. The Concurrent AIX Update feature for AIX V6.1
allows fixes to the base kernel and kernel extensions to be applied and simultaneously
become fully operational on a running system. The system does not require any subsequent
reboot to activate fixes. Concurrent AIX Update’s ability to update a running system provides
the following significant advantages:
► The ability to apply either preventive maintenance or corrective service fix without
requiring a reboot
► The ability to reject an applied fix without requiring a reboot
► The ability to inject diagnostics or temporary circumventions without requiring a reboot
► Encouraging customer adoption of corrective service fixes, thereby decreasing outages
for which fixes existed, but which would not have formerly been applied, due to the
disruption to availability by the prior update scheme
► Improved system uptime
► Improved customer satisfaction
► A more convenient approach
Concurrent AIX Update enables activation and deactivation of IBM fixes to the kernel and
kernel extensions. It accomplishes this by adding new capabilities to the interim fix packaging
and installation tools, the system loader, and to the system process component.
Note: The ability to apply or remove a fix without the requirement of a reboot is limited to
Concurrent AIX Updates. Technological restrictions prevent some fixes from being made
available as a Concurrent AIX Update. In such cases, those fixes may be made available
as an interim fix (that is, “traditional” ifix).
Traditional interim fixes for the kernel or kernel extensions still require a reboot of the
operating system for both activation and removal.
Performing live updates on an operating system is a complicated task, and it places stringent
demands on the operating system. There are many different approaches available for
patching the operating system kernel. Concurrent AIX Update uses a method of functional
redirection within the in-memory image of the operating system to accomplish patching-in of
corrected code. After a fix for a problem has been determined, the corrected code is built,
packaged, and tested according to a new process for Concurrent AIX Update. It is then
provided to the customer, using the existing interim fix package format.
The package will contain one or more object files, and their corresponding executable
modules. Patch object files have numerous restrictions, including (but not limited to) that no
non-local data be modified, and that changes to multiple functions are only permitted if they
34 IBM AIX Continuous Availability Features