How to Enable Image Cache in Block Storage

Problem

Creating volumes from images can be slow, especially when the same image is used repeatedly. This can lead to increased I/O load and longer provisioning times. Enabling image caching in PCD's Block Storage (Cinder) service can significantly improve performance by storing a cached copy of frequently used images.

Environment

• Private Cloud Director Virtualization - v2025.4 and Higher
• Private Cloud Director Kubernetes – v2025.4 and Higher
• Self-Hosted Private Cloud Director Virtualization - v2025.4 and Higher
• Self-Hosted Private Cloud Director Kubernetes - v2025.4 and Higher

Procedure

1. Edit Cinder Backend Configuration: On the host where the Persistent Storage (or Cinder Volume) role is enabled, add the following parameters in the [DEFULT] section of the /opt/pf9/etc/pf9-cindervolume-base/conf.d/cinder.conf

image_volume_cache_enabled
image_volume_cache_max_count
image_volume_cache_max_size_gb

Adjust image_volume_cache_max_count and image_volume_cache_max_size_gb based on the available disk space and use case.

For Example:

image_volume_cache_enabled = True
image_volume_cache_max_count = 50
image_volume_cache_max_size_gb = 200

If NFS is configured as the backend for block storage, then do not enable image caching. Set image_volume_cache_enabled = False to avoid issues related to root disk sizing. (Known issue PCD-2623)

1. After updating the configuration, restart the pf9-cindervolume-base service for the changes to take effect:

$ sudo systemctl restart pf9-cindervolume-base

Validation

Check if Image Cache is Enabled: Verify the effective configuration using the following command on the cinder node:

$ grep image_volume_cache _opt_pf9_etc_pf9-cindervolume-base_conf.d_cinder.conf

Additional Information

What Each Parameter Means:

• image_volume_cache_enabled: Enables or disables the image caching mechanism.
• image_volume_cache_max_count: Limits the number of images to cache. If the limit is reached, the least recently used (LRU) image will be evicted.
• image_volume_cache_max_size_gb: Limits the total size (in GB) of all cached images. The LRU policy also applies here when the limit is hit.