When an unexpected system halt occurs, the system dump facility automatically copies selected areas of kernel data to the primary dump device. These areas include kernel segment 0 as well as other areas registered in the Master Dump Table by kernel modules or kernel extensions. If the dump to the primary dump device fails and you're using AIX release 4.2.1 or later, an attempt is made to dump to the secondary dump device if it has been defined.
When you install the operating system, the dump device is automatically configured for you. By default, the primary device is /dev/hd6, which is a paging logical volume, and the secondary device is /dev/sysdumpnull.
For systems migrated from versions of AIX earlier than 4.1, the primary dump device is what it formerly was, /dev/hd7.
If a dump occurs to paging space, the system will automatically copy the dump when the system is rebooted. By default, the dump is copied to a directory in the root volume group, /var/adm/ras. See the sysdumpdev command for details on how to control dump copying.
Note: Diskless systems automatically configure a remote dump device.