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94 lines
3.9 KiB
Plaintext
94 lines
3.9 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * installing/installing_bare_metal/installing-bare-metal.adoc
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// * installing/installing_bare_metal/installing-bare-metal-network-customizations.adoc
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// * installing/installing_bare_metal/installing-restricted-networks-bare-metal.adoc
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:_mod-docs-content-type: PROCEDURE
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[id="rhcos-enabling-multipath_{context}"]
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= Enabling multipathing with kernel arguments on {op-system}
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{op-system} supports multipathing on the primary disk, allowing stronger resilience to hardware failure to achieve higher host availability.
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You can enable multipathing at installation time for nodes that were provisioned in {product-title} 4.8 or later. While postinstallation support is available by activating multipathing via the machine config, enabling multipathing during installation is recommended.
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In setups where any I/O to non-optimized paths results in I/O system errors, you must enable multipathing at installation time.
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[IMPORTANT]
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====
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On {ibmzProductName} and {linuxoneProductName}, you can enable multipathing only if you configured your cluster for it during installation. For more information, see "Installing {op-system} and starting the {product-title} bootstrap process" in _Installing a cluster with z/VM on {ibmzProductName} and {linuxoneProductName}_.
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====
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// Add xref once it's allowed.
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The following procedure enables multipath at installation time and appends kernel arguments to the `coreos-installer install` command so that the installed system itself will use multipath beginning from the first boot.
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.Prerequisites
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* You have a running {product-title} cluster that uses version 4.8 or later.
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+
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[NOTE]
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====
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{product-title} does not support enabling multipathing as a day-2 activity on nodes that have been upgraded from 4.6 or earlier.
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====
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* You are logged in to the cluster as a user with administrative privileges.
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.Procedure
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. To enable multipath and start the `multipathd` daemon, run the following command:
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+
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[source,terminal]
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----
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$ mpathconf --enable && systemctl start multipathd.service
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----
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** Optional: If booting the PXE or ISO, you can instead enable multipath by adding `rd.multipath=default` from the kernel command line.
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. Append the kernel arguments by invoking the `coreos-installer` program:
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+
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* If there is only one multipath device connected to the machine, it should be available at path `/dev/mapper/mpatha`. For example:
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[source,terminal]
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----
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$ coreos-installer install /dev/mapper/mpatha \ <1>
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--append-karg rd.multipath=default \
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--append-karg root=/dev/disk/by-label/dm-mpath-root \
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--append-karg rw
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----
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<1> Indicates the path of the single multipathed device.
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+
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* If there are multiple multipath devices connected to the machine, or to be more explicit, instead of using `/dev/mapper/mpatha`, it is recommended to use the World Wide Name (WWN) symlink available in `/dev/disk/by-id`. For example:
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[source,terminal]
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----
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$ coreos-installer install /dev/disk/by-id/wwn-<wwn_ID> \ <1>
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--append-karg rd.multipath=default \
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--append-karg root=/dev/disk/by-label/dm-mpath-root \
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--append-karg rw
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----
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<1> Indicates the WWN ID of the target multipathed device. For example, `0xx194e957fcedb4841`.
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This symlink can also be used as the `coreos.inst.install_dev` kernel argument when using special `coreos.inst.*` arguments to direct the live installer. For more information, see "Installing {op-system} and starting the {product-title} bootstrap process".
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. Check that the kernel arguments worked by going to one of the worker nodes and listing the kernel command line arguments (in `/proc/cmdline` on the host):
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[source,terminal]
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----
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$ oc debug node/ip-10-0-141-105.ec2.internal
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----
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.Example output
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[source,terminal]
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----
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Starting pod/ip-10-0-141-105ec2internal-debug ...
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To use host binaries, run `chroot /host`
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sh-4.2# cat /host/proc/cmdline
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...
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rd.multipath=default root=/dev/disk/by-label/dm-mpath-root
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...
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sh-4.2# exit
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----
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You should see the added kernel arguments.
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