Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Booting and Shutdown
Abnormal System Shutdowns
Chapter 5536
When you define your dump devices, whether in a kernel build or at run time,
you can list which classes of memory must always get dumped, and which classes
of memory should not be dumped. If you leave both of these lists empty, HP-UX
will decide for you which parts of memory should be dumped based on what type
of error occurred. In nearly all cases, this is the best thing to do.
NOTE Even if you have defined (in the kernel or at run time) that you do not want a full
dump to be performed, an operator at the system console at the time of a crash
can override those definitions and request a full dump.
Likewise, if at the time of a crash you know what caused it (and therefore do not
need the system dump), but have previously defined a full or selective dump, an
operator at the system console at the time of a crash can override those
definitions and request no dump be performed.
Compressed Dump (HP-UX version 1 (B.11.11) or later) Compressed
dump is a feature available on systems running HP-UX 11i version 1 (or
subsequent releases). Following a system crash, the HP-UX operating system can
use the feature to compress data from memory before it writes the data to the
dump device. Compression decreases the volume of crash data, making the
writes to disk faster.
By reducing the time required to store the entire dump, the recovery period is
shorter and your system will be up and running much more quickly. Dump
compression provides a greater time saving on systems that have large amounts
of memory.
The following features are available in this version of dump compression:
• Dump compression is not forced, it is only a kernel hint.
At the time of a system crash, the dump subsystem examines the state of the
system and its resources to determine whether it is possible to use
compression. Depending on the resources available, the system decides
dynamically whether to dump compressed or uncompressed.
(For example if the processor that is processing the crash fails to assign a
sufficient number of processors to do the compression, the dump will not be
compressed. A recursive crash, such as a panic in dump path, also causes the
system to dump uncompressed.)
• For selective dumps that exclude UNUSED pages, you can expect the dump
to take about one-third the time of uncompressed dumps on the same
system. This interval includes the time required to run the savecrash
program and write the dump to its final storage location on the HP-UX file
system.