HP-UX System Administrator's Guide: Overview

The boot time utility called savecrash can be configured (by editing the file /etc/
rc.config.d/savecrash) to compress or not compress the data as it copies the memory
image from the dump devices to the HP-UX file system area during the reboot process. This
has system recovery time implications in that compressing the data can take longer if
the saving occurs as foreground processing (for example, when HP-UX is trying to
quickly evacuate a dump device that is also used for paging). So, if you have the disk
space and require that your system be back up and running as quickly as possible,
configure savecrash to not compress the data.
Using a Device for Both Paging and Dumping (System Recovery Time)
It is possible to use a specific device for both paging (swap space) and as a dump device.
However, if system recovery time is critical to you do not configure the primary paging
device as a dump device. From the savecrash(1M) manpage:
• “By default, when the primary paging device is not used as one of the dump
devices or after the crash image on the primary paging device has been saved,
savecrash runs in the background. This reduces system boot-up time by allowing
the system to be run with only the primary paging device.”
Another advantage to keeping your paging and dump devices separate is that paging
will not overwrite information stored on a dump device, no matter how long the system
has been up or how much activity has taken place. Therefore, you can prevent
savecrash processing at boot time (by editing the file /etc/rc.config.d/
savecrash). This can save you a lot of time at boot time by allowing you to save the
memory image after the server has been returned to service. After the server is up and
running you can run savecrash manually to copy the memory image from the dump
area to the HP-UX file system area.
Partial Saves
If a memory dump resides partially on dedicated dump devices and partially on devices
that are also used for paging, you can choose to save (to the HP-UX file system) only
those pages that are endangered by paging activity. Pages residing on the dedicated
dump devices can remain there. If you know how to analyze memory dumps, it is even
possible to analyze them directly from the dedicated dump devices using a debugger
that supports this feature.
Before sending your memory dump to someone else for analysis you must move the
dumped pages from the dedicated dump devices to the HP-UX file system. You can
then use a utility such as pax or tar to bundle them up for shipment.
Start-up and Shutdown 99