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Chapter 7 151
Recovering from failures
Abnormal system shutdowns
The fewer pages dumped to disk (and on reboot, copied to the HP-UX file
system area), the faster the system can be back up and running.
Therefore, avoid using the full dump option.
When defining dump devices, whether in a kernel build or at run time,
the operator can list which classes of memory must always get dumped,
and which classes of memory should not be dumped. If both of these
“lists” are left empty, HP-UX decides which parts of memory should be
dumped based on what type of error occurred. In nearly all cases, leaving
the lists empty is preferred.
NOTE Even if a full dump has not been defined (in the kernel or at run time),
the definitions can be overridden (within a ten second window) and a
request for a full dump after a system crash can be performed. Likewise,
if the cause of the crash is known, a request to not dump can be
performed as well.
Compressed save vs. noncompressed save
System dumps can be so large that they tax the HP-UX file system area.
The boot time utility, 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 effects system recovery time
in that data compression takes longer. Therefore, if there is enough disk
space and the fastest system recovery is required, configure savecrash
to not compress the data. See the savecrash(1M) man pages for more
information.
Using a device for both paging and dumping
It is possible to use a specific device for both paging (swapping) and as a
dump device. If system recovery time is critical, do not configure the
primary paging device as a dump device.
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, by
default, savecrash runs in the background. This reduces system boot
time by running the system with only the primary paging device.
Another advantage to keeping paging and dump devices separate is that
paging does not overwrite the information stored on a dump device, no
matter how long the system has been up or how much activity has taken
place. Disabling savecrash processing at boot time (by editing the file