Image Storage Backends

Overview

The Polystack Image Service stores image data in a pluggable storage backend. The selection of backend affects availability, performance, and instance launch times. Multiple backends can be registered simultaneously — administrators select which backend stores each image at upload time. This guide covers configuration of all supported backends via the deployment console globals.

Administrator Access Required — This operation requires the admin role. Contact your Polystack administrator if you do not have sufficient permissions.

Supported Backends

Backend	Use Case	HA	Notes
Distributed Storage (RBD)	Production — fast clones, no single point of failure	Yes	Recommended for all multi-node deployments
File Store	Single-node or development deployments	No	Default backend; not HA
Polystack Object Storage (Swift)	Scalable distributed image storage	Yes	Suitable when Swift is already deployed
S3-Compatible	AWS S3 or S3-compatible object stores	Yes	Works with AWS, Ceph RGW, MinIO, Dell ECS
VMware Datastore	VMware vSphere integration environments	Yes	Stores images directly in vSphere datastores
Cinder (Block Storage)	Block storage as image store	Yes	Volumes used as image backing devices
HTTP (read-only)	Remote image sources without upload	N/A	Read-only; images fetched from external URLs

Polystack Distributed Storage (RBD) — Recommended

RBD (RADOS Block Device) is the recommended backend for high-availability multi-node deployments. Images are stored as RBD objects in the Polystack Distributed Storage cluster, providing built-in redundancy and copy-on-write clones for fast instance launches.

Configure RBD backend in the deployment console globals

RBD storage backend configuration

glance_backend_ceph: "yes"
glance_backend_file: "no"
ceph_glance_keyring: ceph.client.glance.keyring
ceph_glance_pool_name: images

Deploy the configuration

Apply glance configuration

ironcore-ansible deploy --tags glance

Verify the images pool exists

Verify RBD pool

ceph osd pool ls | grep images

The images pool appears in the Ceph pool list.

When using RBD as the image backend and RBD as the volume backend, instance launches perform a zero-copy RBD clone from the image pool into the volume pool — resulting in near-instantaneous boot times regardless of image size.

File Store

The file store writes image data to a local or NFS-mounted directory. It is the default backend and suitable for single-node deployments.

File store configuration

glance_backend_file: "yes"
glance_file_datadir_volume: glance

The image directory is mounted as a Docker named volume (glance) accessible at /var/lib/glance/images/ inside the Image API container. To store images in a custom directory (e.g., on a dedicated volume):

glance-api.conf — custom directory

[glance_store]
default_backend = file
filesystem_store_datadir = /mnt/glance_images/

Prepare the host path with the correct ownership:

Prepare custom image directory

mkdir -p /mnt/glance_images/
chown 42424:42424 /mnt/glance_images/

Apply the configuration:

Apply glance configuration

ironcore-ansible reconfigure --tags glance

The file store is not highly available. If the node running the Image API fails, images stored locally are unavailable until the node recovers. Use RBD for production HA deployments.

Polystack Object Storage (Swift)

Images can be stored in Polystack Object Storage (Swift) containers. This backend is suitable when Object Storage is already deployed and disk-to-disk copy overhead is acceptable.

Swift storage backend configuration

glance_backend_swift: "yes"
glance_backend_file: "no"
glance_swift_store_container: glance
glance_swift_store_create_container_on_put: "true"

The full glance-api.conf parameters for Swift:

glance-api.conf — Swift backend

[glance_store]
default_backend = swift
swift_store_auth_address = http://10.0.1.71:5000/v3
swift_store_user = service:glance
swift_store_key = <glance-service-password>
swift_store_container = glance
swift_store_create_container_on_put = true
swift_store_multi_tenant = false

S3-Compatible Object Storage

The S3 backend driver supports any S3-compatible endpoint including AWS S3, Ceph RADOS Gateway, MinIO, and Dell ECS. This enables off-site or cloud-based image storage.

glance-api.conf — S3 backend

[glance_store]
default_backend = s3
s3_store_host = https://s3.example.com
s3_store_access_key = <access-key>
s3_store_secret_key = <secret-key>
s3_store_bucket = glance-images
s3_store_create_bucket_on_put = true
s3_store_large_object_size = 100
s3_store_large_object_chunk_size = 10

Apply via the deployment console globals:

the deployment console globals — S3 backend

glance_backend_s3: "yes"
glance_backend_file: "no"
glance_s3_store_host: "https://s3.example.com"
glance_s3_store_access_key: "<access-key>"
glance_s3_store_secret_key: "<secret-key>"
glance_s3_store_bucket: "glance-images"

VMware Datastore

The VMware datastore backend stores images in vSphere datastores. This is required when the compute layer uses the VMware vSphere driver and images must reside on vCenter-managed datastores.

glance-api.conf — VMware datastore backend

[glance_store]
default_backend = vsphere
vmware_server_host = 10.0.10.20
vmware_server_username = administrator@vsphere.local
vmware_server_password = <password>
vmware_datastores = DatacenterName:DatastoreName:100
vmware_store_image_dir = /openstack_glance
vmware_api_insecure = false
vmware_task_poll_interval = 5

The vmware_datastores value follows the format DatacenterName:DatastoreName:Weight. Multiple datastores can be listed to distribute images across datastores.

Cinder (Block Storage as Image Store)

The Cinder backend stores images as Cinder volumes. Each image is backed by a block volume in the configured Cinder pool. This backend is useful when block storage is the primary shared storage medium.

glance-api.conf — Cinder backend

[glance_store]
default_backend = cinder
cinder_catalog_info = volumev3::internalURL
cinder_volume_type = image-store
cinder_store_user_name = glance
cinder_store_auth_address = http://10.0.1.71:5000/v3
cinder_store_project_name = service

The Cinder volume type (image-store) must exist and map to a backend with sufficient capacity.

HTTP (Read-Only Remote)

The HTTP backend allows the Image Service to serve images stored at external URLs without downloading or storing them locally. This backend is read-only — images cannot be uploaded through the HTTP backend.

glance-api.conf — HTTP backend

[glance_store]
default_backend = http

To add an image from a remote URL:

openstack image create \
  --disk-format qcow2 \
  --container-format bare \
  --location http://example.com/images/ubuntu-24.04.qcow2 \
  ubuntu-24.04-remote

Images registered with the HTTP backend depend on the availability of the remote URL. If the URL becomes unreachable, image-backed instances cannot be launched. Use this backend only for read-only catalog images or testing.

Verify Backend Configuration

After deployment, confirm the Image API is using the expected backend:

Check Image API configuration

docker exec glance_api grep -A 5 "\[glance_store\]" /etc/glance/glance-api.conf

Upload a test image and verify storage

openstack image create \
  --disk-format qcow2 \
  --container-format bare \
  --file /dev/zero \
  --min-disk 1 \
  test-backend-check

Check RBD pool contents (if using RBD)

rbd ls images

Next Steps

Architecture

Understand how the storage backend fits into the overall Image Service topology.

Image Templates

Use images as templates, manage catalogs, and export images.

Image Cache

Layer a local cache over your storage backend to reduce launch times.

Admin Troubleshooting

Diagnose storage connectivity and upload failure issues.

Core Services

Other Services

Overview

Supported Backends

Polystack Distributed Storage (RBD) — Recommended

Configure RBD backend in the deployment console globals

Deploy the configuration

Verify the images pool exists

File Store

Polystack Object Storage (Swift)

S3-Compatible Object Storage

VMware Datastore

Cinder (Block Storage as Image Store)

HTTP (Read-Only Remote)

Verify Backend Configuration

Next Steps

Architecture

Image Templates

Image Cache

Admin Troubleshooting

​Overview

​Supported Backends

​Polystack Distributed Storage (RBD) — Recommended

Configure RBD backend in the deployment console globals

Deploy the configuration

Verify the images pool exists

​File Store

​Polystack Object Storage (Swift)

​S3-Compatible Object Storage

​VMware Datastore

​Cinder (Block Storage as Image Store)

​HTTP (Read-Only Remote)

​Verify Backend Configuration

​Next Steps

Architecture

Image Templates

Image Cache

Admin Troubleshooting

Overview

Supported Backends

Polystack Distributed Storage (RBD) — Recommended

File Store

Polystack Object Storage (Swift)

S3-Compatible Object Storage

VMware Datastore

Cinder (Block Storage as Image Store)

HTTP (Read-Only Remote)

Verify Backend Configuration

Next Steps