32.4. Using fadump on IBM PowerPC hardware
Starting with Red Hat Enterprise Linux 6.8 an alternative dumping mechanism to
fadump), is available. The
fadumpfeature is supported only on IBM Power Systems. The goal of
fadumpis to enable the dump of a crashed system, and to do so from a fully-reset system, and to minimize the total elapsed time until the system is back in production use. The
fadumpfeature is integrated with
kdumpinfrastructure present in the user space to seemlessly switch between
Firmware-assisted dump (
fadump) is a reliable alternative to
kexec-kdumpavailable on IBM PowerPC LPARS. It captures vmcore from a fully-reset system with PCI and I/O devices reinitialized. While this mechanism uses the firmware to preserve the memory in case of a crash, it reuses the
kdumpuserspace scripts to save the vmcore"
To achieve this,
fadumpregisters the regions of memory that must be preserved in the event of a crash with the system firmware. These regions consist of all the system memory contents, except the boot memory, system registers and hardware Page Table Entries (PTEs).
The area of memory not preserved and known as
boot memoryis the amount of RAM required to successfully boot the kernel after a crash event. By default, the boot memory size is 256MB or 5% of total system RAM, whichever is larger.
kexec-initiated event, the
fadumpprocess uses the production kernel to recover a crash dump. When booting after a crash, PowerPC hardware makes the device node
procfs, which the fadump-aware
kdumpscripts check for to save the vmcore. After this has completed, the system is rebooted cleanly.
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/swap crashkernel=auto rd.lvm.lv=rhel/root rhgb quiet
- (optional) If you want to specify reserved boot memory instead of accepting the defaults, add
/etc/default/grub, where xx is the amount of the memory required in megabytes:
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/swap crashkernel=auto rd.lvm.lv=rhel/root rhgb quiet fadump=on
As with all boot configuration options, it is strongly recommended that you test the configuration before it is needed. If you observe Out of Memory (OOM) errors when booting from the crash kernel, increase the value specified in
fadump_reserve_mem=until the crash kernel can boot cleanly. Some trial and error may be required in this case.