Firmware-assisted dumps

in AIX

Firmware-assisted dumps

System dumps can be very useful when your system crashes or restarts unexpectedly. It helps IBM support or application owners to investigate the root cause of the crash. A system dump creates a picture of your system's memory contents. It can be also manually initiated by system users (with root authority) and programmers and thus analyze its contents when debugging new applications.

A new feature of AIX V7.1 and AIX 6.1 and POWER6 and POWER7 processor-based systems is the Firmware-assisted dump.

The difference from traditional system dumps is that firmware-assisted dumps are not generated before the partition is reinitialized but take place when the partition is restarting. When performing a firmware-assisted dump, system memory is frozen and the partition rebooted, which allows a new instance of the operating system to dump data from the previous kernel crash. Firmware-assisted dumps are more reliable because they minimize the role of the failing AIX instance in collecting data. However they are suitable only when the system has more than 1.5 GB of memory.

Firmware-assisted dump requires:

  • A POWER6 processor-based or later hardware platform
    (Firmware-assisted dump may be configured on POWER5™ or earlier based hardware, but all system dumps will operate as traditional dump).
  • The LPAR must have a minimum of 1.5 GB memory.
  • The dump logical volume must be in the root volume group.
  • Paging space cannot be defined as the dump logical volume.

Firmware-assisted dump is the default dump type in AIX V7.1 when the hardware platform supports firmware-assisted dump (POWER6 and POWER7). The traditional dump is the default dump type for AIX V6.1.

The output of sysdumpdev -l command from the default installation setting of both AIX 6.1 and AIX 7.1 can be seen below:

AIX 6.1

# sysdumpdev -l

primary                          /dev/lg_dumplv

secondary                        /dev/sysdumpnull

copy directory                   /var/adm/ras

forced copy flag                 TRUE

always allow dump                FALSE

dump compression                 ON

type of dump                     traditional

AIX 7.1

# sysdumpdev -l

primary                          /dev/lg_dumplv

secondary                        /dev/sysdumpnull

copy directory                   /var/adm/ras

forced copy flag                 TRUE

always allow dump                FALSE

dump compression                 ON

type of dump                     fw-assisted

full memory dump                 disallow

The firmware-assisted dump may be changed to traditional dump with the following command:

# sysdumpdev -t traditional

Changing from firmware-assisted to traditional dump will take effect immediately and does not require a reboot of the partition.

or switch back to firmware-assisted dump:

# sysdumpdev -t fw-assisted

Changing from traditional to firmware-assisted dump requires a reboot of the partition for the dump changes to take effect.

When firmware-assisted dump is enabled, there is one more option available - full memory dump (seen with sysdumpdev -l).

The administrator can configure firmware-assisted dump to allow, disallow, or require the dump of the full system memory or kernel memory with the sysdumpdev -f keyword command.

The following keywords are accepted (depending on the AIX version the kernel option may be not available):

  • The disallow keyword specifies that neither the full memory system dump mode nor the kernel memory system dump mode is allowed. Only selected portion of the memory will be dumped. This is the default and most widely used option.
  • The allow_full keyword specifies that the full memory system dump mode is allowed but is performed only when operating system cannot properly handle the dump request.
  • The allow_kernel keyword specifies that the kernel memory system dump mode is allowed but is performed only when operating system cannot properly handle the dump request.
  • The require_full keyword specifies that the full memory system dump mode is always performed.
  • The require_kernel keyword specifies that firmware-assisted system dump of kernel memory is always performed.

For general recommendation of configuring system dump devices see Setting up your AIX dump device.


tags: FW-assisted dumps, system dumps


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