Using A Device For Both Paging And As A Dump Device - HP 9000 V-Class Operator's Manual

Recovering from failures
Abnormal system shutdowns
Example
A system called appserver has 1 Gbyte of physical memory. If you were to
define dump devices for this system with a total of 256 Mbytes of space in
the kernel file and then define an additional 768 Mbytes of disk space in
the /etc/fstab file, you would have enough dump space to hold the
entire memory image (a full dump).
If the crash occurs, however, before /etc/fstab is processed, only the
amount of dump space already configured is available at the time of the
crash; in this example, it is 256 Mbytes of space.
Define enough dump space in the kernel configuration if it is critical to
capture every byte of memory in all instances, including the early stages
of the boot process.
This example is presented for completeness. The actual amount of time
NOTE
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 practically
nonexistent.

Using a device for both paging and as a dump device

It is possible to use a specific device for both paging purposes and as a
dump device. If, however, crash dump integrity is critical, this is not
recommended.
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 indicates 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.
Systems configured with small amounts of memory and using only the
primary swap device as a dump device might not be able to preserve the
dump (copy it to the HP-UX file system area) before paging activity
destroys the data in the dump area. Larger memory systems are less
likely to need paging (swap) space during start-up and are therefore less
likely to destroy a memory dump on the primary paging device before it
can be copied.
86 Chapter 7