installation-disk-partitioning.adoc

Disk partitioning

In most cases, data partitions are originally created by installing {op-system}, rather than by installing another operating system. In such cases, the {product-title} installer should be allowed to configure your disk partitions.

However, there are two cases where you might want to intervene to override the default partitioning when installing an {product-title} node:

• Create separate partitions: For greenfield installations on an empty disk, you might want to add separate storage to a partition. This is officially supported for making /var or a subdirectory of /var, such as /var/lib/etcd, a separate partition, but not both.

  Important

  For disk sizes larger than 100GB, and especially disk sizes larger than 1TB, create a separate /var partition. See "Creating a separate /var partition" and this Red Hat Knowledgebase article for more information.

  Important

  Kubernetes supports only two file system partitions. If you add more than one partition to the original configuration, Kubernetes cannot monitor all of them.

• Retain existing partitions: For a brownfield installation where you are reinstalling {product-title} on an existing node and want to retain data partitions installed from your previous operating system, there are both boot arguments and options to coreos-installer that allow you to retain existing data partitions.

Creating a separate /var partition

In general, disk partitioning for {product-title} should be left to the installer. However, there are cases where you might want to create separate partitions in a part of the filesystem that you expect to grow.

{product-title} supports the addition of a single partition to attach storage to either the /var partition or a subdirectory of /var. For example:

• /var/lib/containers: Holds container-related content that can grow as more images and containers are added to a system.

• /var/lib/etcd: Holds data that you might want to keep separate for purposes such as performance optimization of etcd storage.

• /var: Holds data that you might want to keep separate for purposes such as auditing.

  Important

  For disk sizes larger than 100GB, and especially larger than 1TB, create a separate /var partition.

Storing the contents of a /var directory separately makes it easier to grow storage for those areas as needed and reinstall {product-title} at a later date and keep that data intact. With this method, you will not have to pull all your containers again, nor will you have to copy massive log files when you update systems.

Because /var must be in place before a fresh installation of {op-system-first}, the following procedure sets up the separate /var partition by creating a machine config manifest that is inserted during the openshift-install preparation phases of an {product-title} installation.

Procedure

1. Create a directory to hold the {product-title} installation files:

   $ mkdir $HOME/clusterconfig

2. Run openshift-install to create a set of files in the manifest and openshift subdirectories. Answer the system questions as you are prompted:

   $ openshift-install create manifests --dir $HOME/clusterconfig
   ? SSH Public Key ...
   $ ls $HOME/clusterconfig/openshift/
   99_kubeadmin-password-secret.yaml
   99_openshift-cluster-api_master-machines-0.yaml
   99_openshift-cluster-api_master-machines-1.yaml
   99_openshift-cluster-api_master-machines-2.yaml
   ...

3. Create a Butane config that configures the additional partition. For example, name the file $HOME/clusterconfig/98-var-partition.bu, and set the storage size as appropriate. This example places the /var directory on a separate partition on the boot disk:

   variant: openshift
   version: {product-version}.0
   metadata:
     labels:
       machineconfiguration.openshift.io/role: worker
     name: 98-var-partition
   storage:
     disks:
     - device: /dev/disk/by-id/coreos-boot-disk
       partitions:
       - label: var
         start_mib: <partition_start_offset>
         size_mib: <partition_size>
         number: 5
     filesystems:
       - device: /dev/disk/by-partlabel/var
         path: /var
         format: xfs
         mount_options: [defaults, prjquota]
         with_mount_unit: true

   where:

   start_mib

   Specifies the starting offset of a disk partition in mebibytes (MiB). When adding a data partition to the boot disk, a minimum value of 25000 MiB is recommended. The root file system is automatically resized to fill all available space up to the specified offset. If no value is specified, or if the specified value is smaller than the recommended minimum, the resulting root file system will be too small, and future reinstalls of {op-system} might overwrite the beginning of the data partition.

   size_mib

   Specifies the size of the data partition in mebibytes (MiB).

   mount_options

   Specifies the configurable mount options available. The prjquota mount option must be enabled for filesystems used for container storage.

   Note	When creating a separate /var partition, you cannot use different instance types for worker nodes, if the different instance types do not have the same device name.

4. Create a manifest from the Butane config and save it to the clusterconfig/openshift directory. For example, run the following command:

   $ butane $HOME/clusterconfig/98-var-partition.bu -o $HOME/clusterconfig/openshift/98-var-partition.yaml

5. Run openshift-install again to create Ignition configs from a set of files in the manifest and openshift subdirectories:

   $ openshift-install create ignition-configs --dir $HOME/clusterconfig
   $ ls $HOME/clusterconfig/
   auth  bootstrap.ign  master.ign  metadata.json  worker.ign

Now you can use the Ignition config files as input to the vSphere installation procedures to install {op-system-first} systems.