Image Library with Multiple Storage Backends
The Private Cloud Director Image Library Service can use more than one storage backend within a region. Each storage backend is a store that holds image data, and you designate one backend as the default. Configuring multiple storage backends lets you keep images on more than one backend, such as a shared filesystem together with one or more block storage volume types.
How It Works
You configure the storage backends, and the default backend, as part of the cluster blueprint image library configuration.
Each storage backend is either a shared filesystem store or a block storage store that is identified by its volume type name.
When you upload an image, the Image Library Service writes it to every configured storage backend, so the image is available from all of them.
The Compute Service and the Persistent Storage Service fetch an image from a storage backend where the image is present.
Supported Storage Backends
Shared filesystem (for example, NFS)
Only one shared filesystem store is supported.
Block storage volume type
Multiple block storage backends are supported. Each backend is identified by a distinct volume type name.
For details on configuring a block storage backend and the shared storage requirement, see Image Library High Availability.
Configure Multiple Storage Backends
You configure the storage backends, and the default backend, in the cluster blueprint image library configuration. Provide each block storage backend by its volume type name, and designate one of the configured backends as the default backend.
Important
You can edit the storage backend configuration only when the Image Library role is deauthorized from the hosts. To add or change storage backends, deauthorize the Image Library role from the hosts, edit the configuration, and then re-authorize the role.
Upload Images
When multiple storage backends are configured, upload images using the pcdctl CLI. An image is written to all configured storage backends so that it is available from each one.
Prerequisites
Install the pcdctl CLI if it is not already installed:
For credential setup, see the Overview.
Upload an image to all storage backends
Run the following command to upload an image and copy it to every configured storage backend:
The --all-stores option copies the image to every configured storage backend after upload.
Manage Storage Backends from the UI
In addition to the cluster blueprint and the pcdctl CLI, you can configure storage backends, upload images, and monitor image replication from the Private Cloud Director UI.
Configure Storage Backends in the Cluster Blueprint
In the cluster blueprint, open Cluster Defaults and go to the Image Library configuration. Each storage backend appears as a store row.
For each store, select a Location: Local File System, Shared File System, or Volume Type.
Provide the value for that location: a Volume Type for a block storage backend, or a File System Path for a filesystem backend.
Select Default on the store that receives the initial upload.
To add another backend, select Add store. To remove a backend, select the remove icon on that store row.
Save the blueprint.
The store editor enforces the requirements described under Constraints and Limitations. In particular, each volume type can be used by only one store, at most one filesystem store (shared or local) can be configured, and a Local File System store can only be used as a single store. When a local filesystem store is selected, you cannot add more stores.
When you save a blueprint that adds a new store and images already exist, the UI prompts you to copy the existing images to all stores. See Copy Existing Images to All Storage Backends below.
Monitor Image Replication
The Images list includes a Stores column that shows where each image is stored. Each configured store appears with a colored status indicator:
Green: the image is stored in that store.
Yellow: the image is currently being copied to that store.
Red: the copy to that store failed.
The column updates automatically while a copy is in progress, so you can watch an image populate additional stores without refreshing the page. If a copy fails, a notification reports the image and the stores it could not reach so that you can retry.
Upload Images from the UI
When you upload an image file from the UI on a site with more than one storage backend, the image is uploaded to the default backend and then copied automatically to all configured backends. You do not select stores and you do not run a separate copy step. If the copy cannot be started, the UI keeps the uploaded image and shows a warning so that you can retry the copy later.
The UI also provides the pcdctl command for uploading from the command line. When more than one storage backend is configured, the command dialog shows both a single-store command and a multi-store command that uses --all-stores. For the interactive upload steps, see Upload an Image Using the UI.
Copy Existing Images to All Storage Backends
You can replicate images that are not yet present in every store without re-uploading them.
In the Images list, select one or more images that are missing from a store or that failed to copy.
Select Copy to all stores.
Confirm the copy. The copies run in the background, and the Stores column updates as each copy completes.
The Copy to all stores action is available only when more than one storage backend is configured and at least one selected image is missing from a store or previously failed to copy. If a copy cannot be started for some images, the UI lists those images so that you can retry them later.
Image Copy Permissions
Copying an image to additional storage backends is a privileged action. The role you hold in the tenant that owns the image determines whether the Copy to all stores action succeeds.
Admin: can copy any image in the tenant to all configured storage backends.
Self-Service User: can copy images that their own tenant owns. Copying an image that another tenant owns and shares into the tenant is not permitted.
ReadOnly: cannot copy images.
Under granular RBAC, copying an image is available to Platform Admin, Service Provider Domain Admin, and Customer Domain Admin.
If your role does not permit the copy, the request is rejected and the image remains in the storage backends where it is already present.
Constraints and Limitations
Multiple storage backends require shared storage. You cannot use multiple storage backends with a local filesystem store.
Only one shared filesystem store is supported. You can configure multiple block storage backends, but at most one shared filesystem backend.
The default backend must be one of the configured backends.
Editing requires the Image Library role to be deauthorized. To add or change storage backends, deauthorize the Image Library role from the hosts first, and then re-authorize the role after the change.
An image is uploaded to all configured backends. Image data is written to every configured storage backend, not to a single backend.
Storage backends apply within a single region. Image data is not replicated across regions.
Related Topics
RBAC Roles and Permissions: what each role can do with images
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