# 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`

```bash
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:

```bash
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)

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

```bash
$ 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:

```bash
$ 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.


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