HP-UX System Administrator's Guide: Overview

Example 3-5 Example of a Crash During the Very Early Stages of the Boot Process
Consider a server that has ten gigabytes (10 GB) of physical memory. If you were to
define system dump devices with a total of two gigabytes (2 GB) of space in the kernel
file, and then define an additional nine gigabytes (9 GB) of disk space in the /etc/
fstab file, you would have enough dump space to hold the entire memory image (a
full dump) by the time the system was fully up and running.
But, what if a crash occurs before /etc/fstab is processed? Only the amount of dump
space already configured will be available at the time of the crash; in this example, two
gigabytes of space.
If it is critical to you to capture every byte of memory in all instances, including the early
stages of the boot process, use crashconf with the -s option (which tells crashconf
to retain dump device definitions across reboots) to define enough dump space in
advance to account for this. crashconf is the preferred method for defining dump
devices in HP-UX 11i version 3.
NOTE: The preceding example is presented for completeness. The actual amount of
time between the point where kernel dump devices are activated, and the point where
runtime dump devices are activated is very small (a few seconds), so the window of
vulnerability for this situation is very small.
Using a Device for Both Paging and Dumping (Crash Integrity)
It is possible to use a specific device for both paging purposes and as a dump device.
But, if crash dump integrity is critical to you, this is not recommended. From the
savecrash(1M) manpage:
• “If savecrash determines that a dump device is already enabled for paging, and
that paging activity has already taken place on that device, a warning message
will indicate that the dump may be invalid. If a dump device has not already been
enabled for paging, savecrash prevents paging from being enabled to the device
by creating the file /etc/savecore.LCK. swapon does not enable the device for
paging if the device is locked in /etc/savecore.LCK.”
So, if possible, avoid using a given device for both paging and dumping: particularly
the primary paging device!
HP-UX systems configured with small amounts of memory and using only the primary
swap device as a dump device are in danger of not being able to preserve the dump
(copy it to the HP-UX file system area) before paging activity destroys the data in the
dump area. HP-UX systems configured with larger amounts of memory are less likely
to need paging (swap) space during startup, and are therefore less likely to destroy a
memory dump on the primary paging device before it can be copied.
Start-up and Shutdown 101