HP-UX System Administrator's Guide: Overview

The dump process exists so that you have a way of capturing what your system was
doing at the time of a crash. This is not for recovery purposes; processes cannot resume
where they left off following a system crash. Rather, this is for analysis purposes in
order to help you determine why the system crashed and hopefully prevent it from
happening again.
If you want to be able to capture the memory image of your system when a crash occurs
(for later analysis), you need to define in advance the location(s) where HP-UX will
put that image at the time of the crash. This location can be on local disk devices or
logical volumes.
Wherever you decide that HP-UX should put the dump, it is important to have enough
space at the dump location (see “How Much Dump Space You Need” (page 95)). If
you do not have enough space, not every page selected to be dumped will be saved
and you might not capture the part of memory that contains the instruction or data
that caused the crash.
If necessary, you can define more than one dump device so that if the first one fills up,
the next one is used to continue the dumping process until the dump is complete or
no more defined space is available. Beginning with HP-UX 11i version 3 you can even
configure multiple dump devices to be written to in parallel (rather than one after the
other), significantly cutting down dump times.
How Much Dump Space You Need
To guarantee that you have enough dump space, define a dump area that is at least as
big as your computer’s physical memory, plus one megabyte. If you are doing a selective
dump (which is the default dump mode in most cases), much less dump space will
actually be needed. Full dumps require dump space equal to the size of your computer’s
memory plus a little extra for header information.
In HP-UX Release 11i compressed dumps are enabled by default, however, dump
compression will only occur if conditions in the crash environment are favorable. Do
not plan your dump storage space based on potential compression; allow enough space
for an uncompressed full or selective dump. For more information on compressed
dumps, see “Compressed Dumps” (page 97).
Dump Configuration Decisions
As computers continue to grow in speed and processing power, they also tend to grow
in physical memory size. Where once a system with 256MB of memory was considered
to be a huge system, today it is barely adequate for most tasks. Some of today’s HP-UX
systems can have terabytes of memory. This is important to consider because the larger
the size of your computer’s physical memory the longer it will take to dump its contents
following a system crash (and the more disk space the dump will consume).
Usually, when your system crashes it is important to get it back up and running as fast
as possible. If your computer has a very large amount of memory, the time it takes to
dump that memory to disk might be unacceptably long when you are trying to get the
Start-up and Shutdown 95