Specify the Storage Type for VM Ephemeral Disks

You can specify the ephemeral storage type for virtual machines (VMs) by using a flavor with the appropriate extra specification.

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Note

On a system with one or more single-disk compute hosts, do not use ephemeral disks for any VMs unless all single-disk compute hosts are configured to use remote Ceph backing. For more information, see OpenStack Introduction:

Each new flavor is automatically assigned a Storage Type extra spec that specifies, as the default, instantiation on compute hosts configured for image-backed local storage (Local CoW Image Backed). You can change the extra spec to specify instantiation on compute hosts configured for Ceph-backed remote storage, if this is available (Remote Storage Backed). Ceph-backed remote storage is available only on systems configured with a Ceph storage backend.

The designated storage type is used for ephemeral disk and swap disk space, and for the root disk if the virtual machine is launched using boot-from-image. Local storage is allocated from the Local Volume Group on the host, and does not persist when the instance is terminated. Remote storage is allocated from a Ceph storage pool configured on the storage host resources, and persists until the pool resources are reallocated for other purposes. The choice of storage type affects migration behavior; for more information, see StarlingX Storage Configuration and Management: VM Storage Settings for Migration, Resize, or Evacuation.

If the instance is configured to boot from volume, the root disk is implemented using persistent Cinder-based storage allocated from the controller (for a system using LVM) or from storage hosts (for a system using Ceph) by default. On a system that offers both LVM and Ceph storage backends for Cinder storage, you can specify to use the LVM backend when you launch an instance.

To specify the type of storage offered by a compute host, see StarlingX Storage Configuration and Management: Work with Local Volume Groups.

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Caution

Unlike Cinder-based storage, ephemeral storage does not persist if the instance is terminated or the compute node fails.

In addition, for local ephemeral storage, migration and resizing support depends on the storage backing type specified for the instance, as well as the boot source selected at launch.

To change the storage type using the Web administration interface, click Edit for the existing Storage Type extra specification, and select from the Storage drop-down menu.