> For the complete documentation index, see [llms.txt](https://platform9.com/kb/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://platform9.com/kb/pmo/frequently-asked-questions/how-to-calculate-the-block-storage-usage-in-openstack.md).

# How to calculate the block storage usage in Openstack

## Problem

* How to calculate the block storage usage, free/total capacity, and oversubscription ratio using OpenStack Cinder metrics.

{% hint style="info" %}
**Info**

This article explains how to calculate the block storage usage from `cinder get-pools --detail` in OpenStack. It is applicable for **any Cinder backend** (e.g., Ceph, HPE 3PAR, NetApp, etc.) and helps you interpret key metrics related to block storage usage, provisioning, and backend status.
{% endhint %}

## Environment

* Platform9 Managed OpenStack - v4.0 and Higher
* Cinder

## Key Terms

| Term                       | Description                                                                                           |
| -------------------------- | ----------------------------------------------------------------------------------------------------- |
| Total Capacity             | Physical capacity of the backend storage.                                                             |
| Allocated Capacity         | Actual space used on the backend storage (physical usage).                                            |
| Free Capacity              | Unused portion of physical storage.                                                                   |
| Provisioned Capacity       | Total logical volume size requested by users. May exceed physical space if thin provisioning is used. |
| Oversubscription Ratio     | How much logical capacity is provisioned relative to what's physically used.                          |
| Max Oversubscription Ratio | Configured upper limit of how much Cinder is allowed to oversubscribe the backend.                    |

## Answer

* Source admin.rc file.

{% tabs %}
{% tab title="Bash" %}

```bash
$ source admin.rc
```

{% endtab %}
{% endtabs %}

* Run below command to list all the available cinder pools.

{% tabs %}
{% tab title="Bash" %}

```bash
$ cinder get-pools --detail
```

{% endtab %}
{% endtabs %}

* Example output for Cinder with **Ceph** as backend storage.

{% tabs %}
{% tab title="Bash" %}

```bash
$ cinder get-pools --detail

+-----------------------------+-------------------------------------------------------------------+
| Property                    | Value                                                             |
+-----------------------------+-------------------------------------------------------------------+
| allocated_capacity_gb       | 3132                                                              |
| backend_state               | up                                                                |
| driver_version              | [VERSION]                                                         |
| filter_function             | None                                                              |
| free_capacity_gb            | 36527.21                                                          |
| goodness_function           | None                                                              |
| location_info               | [LOCATION_INFO]                                                   |
| max_over_subscription_ratio | 20.0                                                              |
| multiattach                 | True                                                              |
| name                        | [CINDER_POOL_NAME]                                                |
| provisioned_capacity_gb     | 4532                                                              |
| replication_enabled         | False                                                             |
| reserved_percentage         | 0                                                                 |
| storage_protocol            | ceph                                                              |
| thin_provisioning_support   | True                                                              |
| timestamp                   | [TIMESTAMP]                                                       |
| total_capacity_gb           | 103680.78                                                         |
| vendor_name                 | Open Source                                                       |
| volume_backend_name         | ceph1                                                             |
+-----------------------------+-------------------------------------------------------------------+
.. more
```

{% endtab %}
{% endtabs %}

## Calculations

1. Allocated Capacity (Physical Usage)

{% tabs %}
{% tab title="Text" %}

```bash
total_allocated_capacity_gb = sum of allocated_capacity_gb of all cinder pools
```

{% endtab %}
{% endtabs %}

2. Provisioned Capacity (Logical Usage)

{% tabs %}
{% tab title="Text" %}

```bash
total_provisioned_capacity_gb = sum of provisioned_capacity_gb of all cinder pools
```

{% endtab %}
{% endtabs %}

3. Oversubscription Ratio (Actual)

{% tabs %}
{% tab title="Text" %}

```bash
oversubscription_ratio = total_provisioned_capacity_gb / total_allocated_capacity_gb
```

{% endtab %}
{% endtabs %}

4. Free and Total Capacity
   * If all the cinder pools use same backend storage pool.

{% tabs %}
{% tab title="Text" %}

```bash
grand_total_capacity_gb = total_capacity_gb of any one pool
total_free_capacity_gb  = free_capacity_g of any one pool
```

{% endtab %}
{% endtabs %}

```
- If cinder pools use different backend storage pools.
```

{% tabs %}
{% tab title="Text" %}

```bash
grand_total_capacity_gb = sum of total_capacity_gb of all pools
total_free_capacity_gb  = sum of free_capacity_gb of all pools
```

{% endtab %}
{% endtabs %}

5. Maximum Provisioned Capacity Allowed

{% tabs %}
{% tab title="Text" %}

```bash
max_allowed_provisioned_capacity = grand_total_capacity_gb × max_over_subscription_ratio
```

{% endtab %}
{% endtabs %}


---

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