Data Disks

This document describes how to specify data disks to be provisioned and attached to VMs provisioned in Azure.

Azure Machine Data Disks

Azure Machines support optionally specifying a list of data disks to be attached to the virtual machine. Each data disk must have:

• nameSuffix - the name suffix of the disk to be created. Each disk will be named <machineName>_<nameSuffix> to ensure uniqueness.
• diskSizeGB - the disk size in GB.
• managedDisk - (optional) the managed disk for a VM (see below)
• lun - the logical unit number (see below)

Managed Disk Options

See Introduction to Azure managed disks for more information.

Disk LUN

The LUN specifies the logical unit number of the data disk, between 0 and 63. Its value is used to identify data disks within the VM and therefore must be unique for each data disk attached to a VM.

When adding data disks to a Linux VM, you may encounter errors if a disk does not exist at LUN 0. It is therefore recommended to ensure that the first data disk specified is always added at LUN 0.

See Attaching a disk to a Linux VM on Azure for more information.

IMPORTANT! The lun specified in the AzureMachine Spec must match the LUN used to refer to the device in Kubeadm diskSetup. See below for an example.

Ultra disk support for data disks

If we use StorageAccountType as UltraSSD_LRS in Managed Disks, the ultra disk support will be enabled for the region and zone which supports the UltraSSDAvailable capability.

To check all available vm-sizes in a given region which supports availability zone that has the UltraSSDAvailable capability supported, execute following using Azure CLI:

az vm list-skus -l <location> -z -s <VM-size>

Provided that the chosen region and zone support Ultra disks, Azure Machine objects having Ultra disks specified as Data disks will have their virtual machines created with the AdditionalCapabilities.UltraSSDEnabled additional capability set to true. This capability can also be manually set on the Azure Machine spec and will override the automatically chosen value (if any).

When the chosen StorageAccountType is UltraSSD_LRS, caching is not supported for the disk and the corresponding cachingType field must be set to None. In this configuration, if no value is set, cachingType will be defaulted to None.

See Ultra disk for ultra disk performance and GA scope.

Ultra disk support for Persistent Volumes

First, to check all available vm-sizes in a given region which supports availability zone that has the UltraSSDAvailable capability supported, execute following using Azure CLI:

az vm list-skus -l <location> -z -s <VM-size>

Provided that the chosen region and zone support Ultra disks, Ultra disk based Persistent Volumes can be attached to Pods scheduled on specific Azure Machines, provided that the spec field .spec.additionalCapabilities.ultraSSDEnabled on those Machines has been set to true. NOTE: A misconfiguration or lack this field on the targeted Node's Machine will result in the Pod using the PV be unable to reach the Running Phase.

See Use ultra disks dynamically with a storage class for more information on how to configure an Ultra disk based StorageClass and PersistentVolumeClaim.

See Ultra disk for ultra disk performance and GA scope.

Configuring partitions, file systems and mounts

KubeadmConfig makes it easy to partition, format, and mount your data disk so your Linux VM can use it. Use the diskSetup and mounts options to describe partitions, file systems and mounts.

You may refer to your device as /dev/disk/azure/scsi1/lun<i> where <i> is the LUN.

See cloud-init documentation for more information about cloud-init disk setup.

Example

The below example shows how to create and attach a custom data disk "my_disk" at LUN 1 for every control plane machine, in addition to the etcd data disk. NOTE: the same can be applied to worker machines.

kind: KubeadmControlPlane
apiVersion: controlplane.cluster.x-k8s.io/v1beta1
metadata:
  name: "${CLUSTER_NAME}-control-plane"
spec:
    [...]
    diskSetup:
      partitions:
        - device: /dev/disk/azure/scsi1/lun0
          tableType: gpt
          layout: true
          overwrite: false
        - device: /dev/disk/azure/scsi1/lun1
          tableType: gpt
          layout: true
          overwrite: false
      filesystems:
        - label: etcd_disk
          filesystem: ext4
          device: /dev/disk/azure/scsi1/lun0
          extraOpts:
            - "-E"
            - "lazy_itable_init=1,lazy_journal_init=1"
        - label: ephemeral0
          filesystem: ext4
          device: ephemeral0.1
          replaceFS: ntfs
        - label: my_disk
          filesystem: ext4
          device: /dev/disk/azure/scsi1/lun1
    mounts:
      - - LABEL=etcd_disk
        - /var/lib/etcddisk
      - - LABEL=my_disk
        - /var/lib/mydir
---
kind: AzureMachineTemplate
apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
metadata:
  name: "${CLUSTER_NAME}-control-plane"
spec:
  template:
    spec:
      [...]
      dataDisks:
        - nameSuffix: etcddisk
          diskSizeGB: 256
          managedDisk:
            storageAccountType: Standard_LRS
          lun: 0
        - nameSuffix: mydisk
          diskSizeGB: 128
          lun: 1