Configuring a Dump Device

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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.

An attempt is made to dump to a secondary dump device if it has been defined.

Restriction: You cannot use firmware-assisted system dumps for the secondary dump device.

If your system has less than 4 GB of memory, the default dump device is the /dev/hd6 logical volume, which is a paging logical volume. In addition, if the configuration is for a firmware-assisted system dump, you cannot configure the /dev/hd6 logical volume, or any paging space, as the dump device.

Beginning with AIX® 6.1 with the 6100-01 Technology Level, you can configure an iSCSI device as the dump device for a firmware-assisted system dump.

Restriction: You can only use an iSCSI-dump logical volume that resides on the iSCSI boot disk.

Beginning with AIX® 6.1 Technology Level 6100-04, you can perform remote dumps on thin servers. To perform a remote dump on a thin server, you must define the relative dump resource on the NIM master and allocate the related dump resource to the thin server. The dump resource appears as an iSCSI disk to the NIM client and can only be used to configure the primary dump device. You can only configure firmware-assisted system dumps on primary dump devices. See Defining a dump resource for more information.

If a dump occurs to paging space (traditional system dumps only), the system will automatically copy the dump when the system is rebooted. By default, the dump is copied to the /var/adm/ras directory in the root volume group. See the sysdumpdev command for details on how to control dump copying.

Beginning with AIX® 6.1, you can only use compressed dumps. See the sysdumpdev, uncompress command, and dmpuncompress commands for more details.

The dumpcheck facility notifies you if your dump device needs to be larger, or if the file system containing the copy directory is too small. This notification appears in the system error log. If you need to increase the size of your dump device, see Increasing the Size of a Dump Device.

For maximum effectiveness, dumpcheck should be run when the system is most heavily loaded. At such times, the system dump is most likely to be at its maximum size. Also, even with dumpcheck watching the dump size, it may still happen that the dump won't fit on the dump device or in the copy directory at the time it happens. This could occur if there is a peak in system load right at dump time.