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Chapter 1. Fencing Pre-Configuration

This chapter describes tasks to perform and considerations to make before deploying fencing on clusters using Red Hat High Availability Add-On, and consists of the following sections.

1.1. Configuring ACPI For Use with Integrated Fence Devices

If your cluster uses integrated fence devices, you must configure ACPI (Advanced Configuration and Power Interface) to ensure immediate and complete fencing.
If a cluster node is configured to be fenced by an integrated fence device, disable ACPI Soft-Off for that node. Disabling ACPI Soft-Off allows an integrated fence device to turn off a node immediately and completely rather than attempting a clean shutdown (for example, shutdown -h now). Otherwise, if ACPI Soft-Off is enabled, an integrated fence device can take four or more seconds to turn off a node (refer to note that follows). In addition, if ACPI Soft-Off is enabled and a node panics or freezes during shutdown, an integrated fence device may not be able to turn off the node. Under those circumstances, fencing is delayed or unsuccessful. Consequently, when a node is fenced with an integrated fence device and ACPI Soft-Off is enabled, a cluster recovers slowly or requires administrative intervention to recover.

Note

The amount of time required to fence a node depends on the integrated fence device used. Some integrated fence devices perform the equivalent of pressing and holding the power button; therefore, the fence device turns off the node in four to five seconds. Other integrated fence devices perform the equivalent of pressing the power button momentarily, relying on the operating system to turn off the node; therefore, the fence device turns off the node in a time span much longer than four to five seconds.
To disable ACPI Soft-Off, use chkconfig management and verify that the node turns off immediately when fenced. The preferred way to disable ACPI Soft-Off is with chkconfig management: however, if that method is not satisfactory for your cluster, you can disable ACPI Soft-Off with one of the following alternate methods:
  • Changing the BIOS setting to "instant-off" or an equivalent setting that turns off the node without delay

    Note

    Disabling ACPI Soft-Off with the BIOS may not be possible with some computers.
  • Appending acpi=off to the kernel boot command line of the /boot/grub/grub.conf file

    Important

    This method completely disables ACPI; some computers do not boot correctly if ACPI is completely disabled. Use this method only if the other methods are not effective for your cluster.
The following sections provide procedures for the preferred method and alternate methods of disabling ACPI Soft-Off:

1.1.1. Disabling ACPI Soft-Off with chkconfig Management

You can use chkconfig management to disable ACPI Soft-Off either by removing the ACPI daemon (acpid) from chkconfig management or by turning off acpid.

Note

This is the preferred method of disabling ACPI Soft-Off.
Disable ACPI Soft-Off with chkconfig management at each cluster node as follows:
  1. Run either of the following commands:
    • chkconfig --del acpid — This command removes acpid from chkconfig management.
      — OR —
    • chkconfig --level 2345 acpid off — This command turns off acpid.
  2. Reboot the node.
  3. When the cluster is configured and running, verify that the node turns off immediately when fenced.

    Note

    You can fence the node with the fence_node command or Conga.

1.1.2. Disabling ACPI Soft-Off with the BIOS

The preferred method of disabling ACPI Soft-Off is with chkconfig management (Section 1.1.1, “Disabling ACPI Soft-Off with chkconfig Management”). However, if the preferred method is not effective for your cluster, follow the procedure in this section.

Note

Disabling ACPI Soft-Off with the BIOS may not be possible with some computers.
You can disable ACPI Soft-Off by configuring the BIOS of each cluster node as follows:
  1. Reboot the node and start the BIOS CMOS Setup Utility program.
  2. Navigate to the Power menu (or equivalent power management menu).
  3. At the Power menu, set the Soft-Off by PWR-BTTN function (or equivalent) to Instant-Off (or the equivalent setting that turns off the node by means of the power button without delay). Example 1.1, “BIOS CMOS Setup Utility: Soft-Off by PWR-BTTN set to Instant-Off” shows a Power menu with ACPI Function set to Enabled and Soft-Off by PWR-BTTN set to Instant-Off.

    Note

    The equivalents to ACPI Function, Soft-Off by PWR-BTTN, and Instant-Off may vary among computers. However, the objective of this procedure is to configure the BIOS so that the computer is turned off by means of the power button without delay.
  4. Exit the BIOS CMOS Setup Utility program, saving the BIOS configuration.
  5. When the cluster is configured and running, verify that the node turns off immediately when fenced.

    Note

    You can fence the node with the fence_node command or Conga.

Example 1.1. BIOS CMOS Setup Utility: Soft-Off by PWR-BTTN set to Instant-Off

+------------------------------------------|-----------------+
|   ACPI Function             [Enabled]    |  Item Help      |
|   ACPI Suspend Type         [S1(POS)]    |-----------------|
| x Run VGABIOS if S3 Resume  [Auto]       | Menu Level   *  |
|   Suspend Mode              [Disabled]   |                 |
|   HDD Power Down            [Disabled]   |                 |
|   Soft-Off by PWR-BTTN      [Instant-Off]|                 |
|   CPU THRM-Throttling       [50.0%]      |                 |
|   Wake-Up by PCI card       [Enabled]    |                 |
|   Power On by Ring          [Enabled]    |                 |
|   Wake Up On LAN            [Enabled]    |                 |
| x USB KB Wake-Up From S3    [Disabled]   |                 |
|   Resume by Alarm           [Disabled]   |                 |
| x  Date(of Month) Alarm       0          |                 |
| x  Time(hh:mm:ss) Alarm       0 :  0 :   |                 |
|   POWER ON Function         [BUTTON ONLY]|                 |
| x KB Power ON Password       Enter       |                 |
| x Hot Key Power ON           Ctrl-F1     |                 |
+------------------------------------------|-----------------+
This example shows ACPI Function set to Enabled, and Soft-Off by PWR-BTTN set to Instant-Off.

1.1.3. Disabling ACPI Completely in the grub.conf File

The preferred method of disabling ACPI Soft-Off is with chkconfig management (Section 1.1.1, “Disabling ACPI Soft-Off with chkconfig Management”). If the preferred method is not effective for your cluster, you can disable ACPI Soft-Off with the BIOS power management (Section 1.1.2, “Disabling ACPI Soft-Off with the BIOS”). If neither of those methods is effective for your cluster, you can disable ACPI completely by appending acpi=off to the kernel boot command line in the grub.conf file.

Important

This method completely disables ACPI; some computers do not boot correctly if ACPI is completely disabled. Use this method only if the other methods are not effective for your cluster.
You can disable ACPI completely by editing the grub.conf file of each cluster node as follows:
  1. Open /boot/grub/grub.conf with a text editor.
  2. Append acpi=off to the kernel boot command line in /boot/grub/grub.conf (see Example 1.2, “Kernel Boot Command Line with acpi=off Appended to It”).
  3. Reboot the node.
  4. When the cluster is configured and running, verify that the node turns off immediately when fenced.

    Note

    You can fence the node with the fence_node command or Conga.

Example 1.2. Kernel Boot Command Line with acpi=off Appended to It

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/mapper/vg_doc01-lv_root 
#          initrd /initrd-[generic-]version.img
#boot=/dev/hda
default=0
timeout=5
serial --unit=0 --speed=115200
terminal --timeout=5 serial console
title Red Hat Enterprise Linux Server (2.6.32-193.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-193.el6.x86_64 ro root=/dev/mapper/vg_doc01-lv_root console=ttyS0,115200n8 acpi=off
        initrd /initramrs-2.6.32-131.0.15.el6.x86_64.img
In this example, acpi=off has been appended to the kernel boot command line — the line starting with "kernel /vmlinuz-2.6.32-193.el6.x86_64.img".
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