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Merge pull request #70452 from kowen-rh/ocpbugs-12446
OCPBUGS#12446: Update docs to move etcd to a different disk
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‎modules/move-etcd-different-disk.adoc

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You can move etcd from a shared disk to a separate disk to prevent or resolve performance issues.
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.Prerequisites
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* The `MachineConfigPool` must match `metadata.labels[machineconfiguration.openshift.io/role]`. This applies to a controller, worker, or a custom pool.
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* The node's auxiliary storage device, such as `/dev/sdb`, must match the sdb. Change this reference in all places in the file.
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The Machine Config Operator (MCO) is responsible for mounting a secondary disk for {product-title} {product-version} container storage.
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[NOTE]
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====
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This procedure does not move parts of the root file system, such as `/var/`, to another disk or partition on an installed node.
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====
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The Machine Config Operator (MCO) is responsible for mounting a secondary disk for an {product-title} {product-version} container storage.
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.Prerequisites
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Use the following steps to move etcd to a different device:
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* You have installed the {oc-first}.
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* You have access to the cluster with `cluster-admin` privileges.
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* The `MachineConfigPool` must match `metadata.labels[machineconfiguration.openshift.io/role]`. This applies to a controller, worker, or a custom pool.
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.Procedure
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. Create a `machineconfig` YAML file named `etcd-mc.yml` and add the following information:
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. Attach the new disk to the cluster and verify that the disk is detected in the node by using the `lsblk` command in a debug shell:
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+
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[source,terminal]
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----
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$ oc debug node/<node_name>
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----
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[source,terminal]
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----
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# lsblk
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----
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Note the device name of the new disk reported by the `lsblk` command.
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. Create a `MachineConfig` YAML file named `etcd-mc.yml` with contents such as the following, replacing instances of `<new_disk_name>` with the noted device name:
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[source,yaml]
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----
@@ -41,31 +55,31 @@ spec:
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units:
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- contents: |
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[Unit]
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Description=Make File System on /dev/sdb
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Description=Make File System on /dev/<new_disk_name>
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DefaultDependencies=no
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BindsTo=dev-sdb.device
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After=dev-sdb.device var.mount
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Before=systemd-fsck@dev-sdb.service
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BindsTo=dev-<new_disk_name>.device
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After=dev-<new_disk_name>.device var.mount
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Before=systemd-fsck@dev-<new_disk_name>.service
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[Service]
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Type=oneshot
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RemainAfterExit=yes
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ExecStart=/usr/lib/systemd/systemd-makefs xfs /dev/sdb
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ExecStart=/usr/lib/systemd/systemd-makefs xfs /dev/<new_disk_name>
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TimeoutSec=0
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[Install]
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WantedBy=var-lib-containers.mount
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enabled: true
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name: systemd-mkfs@dev-sdb.service
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name: systemd-mkfs@dev-<new_disk_name>.service
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- contents: |
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[Unit]
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Description=Mount /dev/sdb to /var/lib/etcd
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Description=Mount /dev/<new_disk_name> to /var/lib/etcd
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Before=local-fs.target
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Requires=systemd-mkfs@dev-sdb.service
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After=systemd-mkfs@dev-sdb.service var.mount
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Requires=systemd-mkfs@dev-<new_disk_name>.service
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After=systemd-mkfs@dev-<new_disk_name>.service var.mount
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[Mount]
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What=/dev/sdb
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What=/dev/<new_disk_name>
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Where=/var/lib/etcd
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Type=xfs
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Options=defaults,prjquota
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WantedBy=multi-user.target graphical.target
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enabled: true
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name: restorecon-var-lib-etcd.service
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----
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. Create the machine configuration by entering the following commands:
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. Log in to the cluster as a user with `cluster-admin` privileges and create the machine configuration:
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[source,terminal]
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----
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$ oc login -u ${ADMIN} -p ${ADMINPASSWORD} ${API}
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... output omitted ...
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$ oc login -u <username> -p <password>
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----
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[source,terminal]
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$ oc create -f etcd-mc.yml
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machineconfig.machineconfiguration.openshift.io/98-var-lib-etcd created
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----
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[source,terminal]
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----
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$ oc login -u ${ADMIN} -p ${ADMINPASSWORD} ${API}
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[... output omitted ...]
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----
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[source,terminal]
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----
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$ oc create -f etcd-mc.yml machineconfig.machineconfiguration.openshift.io/98-var-lib-etcd created
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----
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The nodes are updated and rebooted. After the reboot completes, the following events occur:
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* An XFS file system is created on the specified disk.
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* The disk mounts to `/var/lib/etc`.
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* The content from `/sysroot/ostree/deploy/rhcos/var/lib/etcd` syncs to `/var/lib/etcd`.
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* A restore of `SELinux` labels is forced for `/var/lib/etcd`.
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* The old content is not removed.
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. After the nodes are on a separate disk, update the machine configuration file, `etcd-mc.yml` with the following information:
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* An XFS file system is created on the specified disk.
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* The disk mounts to `/var/lib/etcd`.
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* The content from `/sysroot/ostree/deploy/rhcos/var/lib/etcd` syncs to `/var/lib/etcd`.
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* A restore of `SELinux` labels is forced for `/var/lib/etcd`.
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* The old content is not removed.
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. After the nodes are on a separate disk, update the `etcd-mc.yml` file with contents such as the following, replacing instances of `<new_disk_name>` with the noted device name:
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[source,yaml]
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----
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units:
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- contents: |
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[Unit]
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Description=Mount /dev/sdb to /var/lib/etcd
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Description=Mount /dev/<new_disk_name> to /var/lib/etcd
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Before=local-fs.target
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Requires=systemd-mkfs@dev-sdb.service
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After=systemd-mkfs@dev-sdb.service var.mount
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Requires=systemd-mkfs@dev-<new_disk_name>.service
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After=systemd-mkfs@dev-<new_disk_name>.service var.mount
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[Mount]
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What=/dev/sdb
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What=/dev/<new_disk_name>
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Where=/var/lib/etcd
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Type=xfs
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Options=defaults,prjquota
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enabled: true
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name: var-lib-etcd.mount
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----
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. Apply the modified version that removes the logic for creating and syncing the device by entering the following command:
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. Apply the modified version that removes the logic for creating and syncing the device to prevent the nodes from rebooting:
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[source,terminal]
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$ oc replace -f etcd-mc.yml
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----
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.Verification steps
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* Run the `grep <new_disk_name> /proc/mounts` command in a debug shell for the node to ensure that the disk mounted:
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The previous step prevents the nodes from rebooting.
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[source,terminal]
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----
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$ oc debug node/<node_name>
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----
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[source,terminal]
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----
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# grep <new_disk_name> /proc/mounts
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----
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.Example output
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[source,terminal]
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----
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/dev/nvme1n1 /var/lib/etcd xfs rw,seclabel,relatime,attr2,inode64,logbufs=8,logbsize=32k,prjquota 0 0
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----

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