|The s390 SCSI dump tool (zfcpdump)
|System z machines (z900 or higher) provide hardware support for creating system
|dumps on SCSI disks. The dump process is initiated by booting a dump tool, which
|has to create a dump of the current (probably crashed) Linux image. In order to
|not overwrite memory of the crashed Linux with data of the dump tool, the
|hardware saves some memory plus the register sets of the boot CPU before the
|dump tool is loaded. There exists an SCLP hardware interface to obtain the saved
|memory afterwards. Currently 32 MB are saved.
|This zfcpdump implementation consists of a Linux dump kernel together with
|a user space dump tool, which are loaded together into the saved memory region
|below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in
|the s390-tools package) to make the device bootable. The operator of a Linux
|system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump
|The user space dump tool accesses the memory of the crashed system by means
|of the /proc/vmcore interface. This interface exports the crashed system's
|memory and registers in ELF core dump format. To access the memory which has
|been saved by the hardware SCLP requests will be created at the time the data
|is needed by /proc/vmcore. The tail part of the crashed systems memory which
|has not been stashed by hardware can just be copied from real memory.
|To build a dump enabled kernel the kernel config option CONFIG_CRASH_DUMP
|has to be set.
|To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig".
|The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs
|under the following locations:
|* kernel: <zfcpdump directory>/zfcpdump.image
|* ramdisk: <zfcpdump directory>/zfcpdump.rd
|The zfcpdump directory is defined in the s390-tools package.
|The user space application of zfcpdump can reside in an intitramfs or an
|initrd. It can also be included in a built-in kernel initramfs. The application
|reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk.
|The s390-tools package version 1.24.0 and above builds an external zfcpdump
|initramfs with a user space application that writes the dump to a SCSI
|For more information on how to use zfcpdump refer to the s390 'Using the Dump
|Tools' book, which is available from IBM Knowledge Center: