IBM AIX Continuous Availability Features - IBM Redbooks

To access the SMIT FFDC menu, use the fastpath smitty ffdc. The menu is shown in
Example 3-1.
Example 3-1 Advanced FFDC features
Advanced First Failure Data Capture Features
Type or select values in entry fields.
Press Enter AFTER making all desired changes.
[Entry Fields]
Advanced First Failure Data Capture Features [enabled] +
Run bosboot automatically [no] +
F1=Help F2=Refresh F3=Cancel F4=List
F5=Reset F6=Command F7=Edit F8=Image
F9=Shell F10=Exit Enter=Do
For more information about FFDC, refer to IBM eServer p5 590 and 595 System Handbook,
SG24-9119.
3.2 Lightweight memory trace
This section describes how to use lightweight memory trace (LMT). Lightweight memory trace
is a serviceability feature. It is an important first failure data capture tool, and is most useful to
those with AIX source-code access or a deep understanding of AIX internals.
3.2.1 LMT implementation
As mentioned, Lightweight memory trace (LMT) provides trace information for First Failure
Data Capture (FFDC). It is a constant kernel trace mechanism that records software events
occurring during system life. The system activates LMT at initialization, and then it runs
continuously. Recorded events are saved to per-processor memory trace buffers.
There are two memory trace buffers for each processor: one to record common events, and
one to record rare events. These buffers can be extracted from system dumps or accessed
on a live system by service personnel using the mtrcsave command. The extracted memory
trace buffers can be viewed by using the trcrpt command, with formatting as defined in the
/etc/trcfmt file.
LMT has been carefully implemented such that it has negligible performance impacts. The
impact on the throughput of a kernel-intensive benchmark is just 1%, and is much less for
typical user workloads. LMT requires the consumption of a small amount of pinned kernel
memory. The default amount of memory required for the trace buffers is calculated based on
factors that influence trace record retention.
Lightweight memory trace differs from traditional AIX system trace in several ways. First, it is
more efficient. Second, it is enabled by default, and has been explicitly tuned as a First
Failure Data Capture mechanism. Unlike traditional AIX system trace, you cannot selectively
record only certain AIX trace hook ids with LMT. With LMT, you either record all LMT-enabled
hooks, or you record none.
Chapter 3. AIX advanced continuous availability tools and features 57