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Hot-plugging VM disks

You can add or remove virtual disks without stopping your virtual machine (VM) or virtual machine instance (VMI).

Only data volumes and persistent volume claims (PVCs) can be hot plugged and hot-unplugged. You cannot hot plug or hot-unplug container disks.

A hot plugged disk remains attached to the VM even after reboot. You must detach the disk to remove it from the VM.

You can make a hot plugged disk persistent so that it is permanently mounted on the VM.

Each VM has a virtio-scsi controller so that hot plugged disks can use the scsi bus. The virtio-scsi controller overcomes the limitations of virtio while retaining its performance advantages. It is highly scalable and supports hot plugging over 4 million disks.

Regular virtio is not available for hot plugged disks because it is not scalable. Each virtio disk uses one of the limited PCI Express (PCIe) slots in the VM. PCIe slots are also used by other devices and must be reserved in advance. Therefore, slots might not be available on demand.

Hot plugging and hot unplugging a disk by using the web console

You can hot plug a disk by attaching it to a virtual machine (VM) while the VM is running by using the OKD web console.

The hot plugged disk remains attached to the VM until you unplug it.

You can make a hot plugged disk persistent so that it is permanently mounted on the VM.

Prerequisites

  • You must have a data volume or persistent volume claim (PVC) available for hot plugging.

Procedure

  1. Navigate to Virtualization → VirtualMachines in the web console.

  2. Select a running VM to view its details.

  3. On the VirtualMachine details page, click Configuration → Disks.

  4. Add a hot plugged disk:

    1. Click Add disk.

    2. In the Add disk (hot plugged) window, select the disk from the Source list and click Save.

  5. Optional: Unplug a hot plugged disk:

    1. Click the options menu kebab beside the disk and select Detach.

    2. Click Detach.

  6. Optional: Make a hot plugged disk persistent:

    1. Click the options menu kebab beside the disk and select Make persistent.

    2. Reboot the VM to apply the change.

Hot plugging and hot unplugging a disk by using the command line

You can hot plug and hot unplug a disk while a virtual machine (VM) is running by using the command line.

You can make a hot plugged disk persistent so that it is permanently mounted on the VM.

Prerequisites

  • You must have at least one data volume or persistent volume claim (PVC) available for hot plugging.

Procedure

  • Hot plug a disk by running the following command:

    $ virtctl addvolume <virtual-machine|virtual-machine-instance> \
  --volume-name=<datavolume|PVC> \
  [--persist] [--serial=<label-name>]

    • Use the optional --persist flag to add the hot plugged disk to the virtual machine specification as a permanently mounted virtual disk. Stop, restart, or reboot the virtual machine to permanently mount the virtual disk. After specifying the --persist flag, you can no longer hot plug or hot unplug the virtual disk. The --persist flag applies to virtual machines, not virtual machine instances.

    • The optional --serial flag allows you to add an alphanumeric string label of your choice. This helps you to identify the hot plugged disk in a guest virtual machine. If you do not specify this option, the label defaults to the name of the hot plugged data volume or PVC.

  • Hot unplug a disk by running the following command:

    $ virtctl removevolume <virtual-machine|virtual-machine-instance> \
  --volume-name=<datavolume|PVC>