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Configuring shared volumes for virtual machines

You can configure shared disks to allow multiple virtual machines (VMs) to share the same underlying storage. A shared disk’s volume must be block mode.

You configure disk sharing by exposing the storage as either of these types:

  • An ordinary virtual machine disk

  • A logical unit number (LUN) device with an iSCSi connection and raw device mapping, as required for Windows Failover Clustering for shared volumes

Configuring disk sharing by using virtual machine disks

You can configure block volumes so that multiple virtual machines (VMs) can share storage.

The application running on the guest operating system determines the storage option you must configure for the VM. A disk of type disk exposes the volume as an ordinary disk to the VM.

Prerequisites

  • The volume access mode must be ReadWriteMany (RWX) if the VMs that are sharing disks are running on different nodes.

    If the VMs that are sharing disks are running on the same node, ReadWriteOnce (RWO) volume access mode is sufficient.

  • The storage provider must support the required Container Storage Interface (CSI) driver.

Procedure

  1. Create the VirtualMachine manifest for your VM to set the required values, as shown in the following example:

    apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: <vm_name>
spec:
  template:
# ...
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: rootdisk
            disk1: disk_one (1)
          - disk:
              bus: virtio
            name: cloudinitdisk
            disk2: disk_two
            shareable: true (2)
          interfaces:
          - masquerade: {}
            name: default
    1 Identifies a device as a disk.
    2 Identifies a shared disk.

  2. Save the VirtualMachine manifest file to apply your changes.

Configuring disk sharing by using LUN

You can configure a LUN-backed virtual machine disk to be shared among multiple virtual machines by enabling SCSI persistent reservation. Enabling the shared option allows you to use advanced SCSI commands, such as those required for a Windows failover clustering implementation, against the underlying storage. Any disk to be shared must be in block mode.

A disk of type LUN exposes the volume as a LUN device to the VM. This allows the VM to execute arbitrary iSCSI command passthrough on the disk.

You reserve a LUN through the SCSI persistent reserve options to protect data on the VM from outside access. To enable the reservation, you configure the feature gate option. You then activate the option on the LUN disk to issue SCSI device-specific input and output controls (IOCTLs) that the VM requires.

Prerequisites

  • You must have cluster administrator privileges to configure the feature gate option.

  • The volume access mode must be ReadWriteMany (RWX) if the VMs that are sharing disks are running on different nodes.

    If the VMs that are sharing disks are running on the same node, ReadWriteOnce (RWO) volume access mode is sufficient.

  • The storage provider must support a Container Storage Interface (CSI) driver that uses the SCSI protocol.

  • If you are a cluster administrator and intend to configure disk sharing by using LUN, you must enable the cluster’s feature gate on the HyperConverged custom resource (CR).

Procedure

  1. Edit or create the VirtualMachine manifest for your VM to set the required values, as shown in the following example:

    apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: vm-0
spec:
  template:
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: sata
            name: rootdisk
          - errorPolicy: report
            lun: (1)
              bus: scsi
              reservation: true (2)
            name: na-shared
            serial: shared1234
      volumes:
      - dataVolume:
          name: vm-0
        name: rootdisk
      - name: na-shared
        persistentVolumeClaim:
          claimName: pvc-na-share
    1 Identifies a LUN disk.
    2 Identifies that the persistent reservation is enabled.

  2. Save the VirtualMachine manifest file to apply your changes.

Configuring disk sharing by using LUN and the web console

You can use the OKD web console to configure disk sharing by using LUN.

Prerequisites

  • The cluster administrator must enable the persistentreservation feature gate setting.

Procedure

  1. Click Virtualization → VirtualMachines in the web console.

  2. Select a VM to open the VirtualMachine details page.

  3. Expand Storage.

  4. On the Disks tab, click Add disk.

  5. Specify the Name, Source, Size, Interface, and Storage Class.

  6. Select LUN as the Type.

  7. Select Shared access (RWX) as the Access Mode.

  8. Select Block as the Volume Mode.

  9. Expand Advanced Settings, and select both checkboxes.

  10. Click Save.

Configuring disk sharing by using LUN and the command line

You can use the command line to configure disk sharing by using LUN.

Procedure

  1. Edit or create the VirtualMachine manifest for your VM to set the required values, as shown in the following example:

    apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: vm-0
spec:
  template:
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: sata
            name: rootdisk
          - errorPolicy: report
            lun: (1)
              bus: scsi
              reservation: true (2)
            name: na-shared
            serial: shared1234
      volumes:
      - dataVolume:
          name: vm-0
        name: rootdisk
      - name: na-shared
        persistentVolumeClaim:
          claimName: pvc-na-share
    1 Identifies a LUN disk.
    2 Identifies that the persistent reservation is enabled.

  2. Save the VirtualMachine manifest file to apply your changes.

Enabling the PersistentReservation feature gate

You can enable the SCSI persistentReservation feature gate and allow a LUN-backed block mode virtual machine (VM) disk to be shared among multiple virtual machines.

The persistentReservation feature gate is disabled by default. You can enable the persistentReservation feature gate by using the web console or the command line.

Prerequisites

  • Cluster administrator privileges are required.

  • The volume access mode ReadWriteMany (RWX) is required if the VMs that are sharing disks are running on different nodes. If the VMs that are sharing disks are running on the same node, the ReadWriteOnce (RWO) volume access mode is sufficient.

  • The storage provider must support a Container Storage Interface (CSI) driver that uses the SCSI protocol.

Enabling the PersistentReservation feature gate by using the web console

You must enable the PersistentReservation feature gate to allow a LUN-backed block mode virtual machine (VM) disk to be shared among multiple virtual machines. Enabling the feature gate requires cluster administrator privileges.

Procedure

  1. Click Virtualization → Overview in the web console.

  2. Click the Settings tab.

  3. Select Cluster.

  4. Expand SCSI persistent reservation and set Enable persistent reservation to on.

Enabling the PersistentReservation feature gate by using the command line

You enable the persistentReservation feature gate by using the command line. Enabling the feature gate requires cluster administrator privileges.

Procedure

  1. Enable the persistentReservation feature gate by running the following command:

    $ oc patch hyperconverged kubevirt-hyperconverged -n kubevirt-hyperconverged \
  --type json -p '[{"op":"replace","path":"/spec/featureGates/persistentReservation", "value": true}]'
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