> 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/solution/unable-to-extend-a-volume.md).

# Unable to Extend a Volume

## Problem

* Extending a volume results in error: "Failed to schedule\_extend\_volume: No valid backend was found."
* The host does not have sufficient space for thin provisioning. The ratio of provisioned capacity over total capacity 1.47 has exceeded the maximum oversubscription ratio 1.00 on host

## Environment

* Platform9 Managed OpenStack - All Versions

## Cause

* Nova-Scheduler log shows "No valid backend was found" error.

{% tabs %}
{% tab title="None" %}

```none
851 13450 WARNING cinder.scheduler.filters.capacity_filter [req-12eb30d8-018e-450c-8bb4-e9e31b54edfa 062abbe158d84dd4a021aa0450a93bbb 0c3c9f76be7c4b08b86313c4f5b745e4 - default default] Insufficient free space for thin provisioning. The ratio of provisioned capacity over total capacity 1.57 has exceeded the maximum over subscription ratio 1.00 on host 166ae366-a3a3-4762-816b-b7c5bc073fdb@netapp_standard#10.81.85.20:/cinder01.889 13450 ERROR cinder.scheduler.manager [req-12eb30d8-018e-450c-8bb4-e9e31b54edfa 062abbe158d84dd4a021aa0450a93bbb 0c3c9f76be7c4b08b86313c4f5b745e4 - default default] Failed to schedule_extend_volume: No valid backend was found. Cannot place volume 02c2161f-8cb7-4ab9-ab15-b9981a73df6f on 166ae366-a3a3-4762-816b-b7c5bc073fdb@netapp_standard#10.81.85.20:/cinder03: NoValidBackend: No valid backend was found. Cannot place volume 02c2161f-8cb7-4ab9-ab15-b9981a73df6f on 166ae366-a3a3-4762-816b-b7c5bc073fdb@netapp_standard#10.81.85.20:/cinder03
```

{% endtab %}
{% endtabs %}

* On the host, we can see that the ***max\_over\_subscription\_ratio*** is set to ***"1"*** in / *opt/pf9/etc/pf9-cindervolume-base/conf.d.*

{% tabs %}
{% tab title="None" %}

```none
[pf9@pdc-h-sdnp9os03 conf.d]$ grep max_over_subscription_ratio /opt/pf9/etc/pf9-cindervolume-base/conf.d/cinder_overrides.confmax_over_subscription_ratio = 1.0
```

{% endtab %}
{% endtabs %}

## Resolution

1. The host does not have sufficient space to extend the volume. Add additional capacity to further extend the volume.

## Additional Information

[OpenStack documentation](https://docs.openstack.org/cinder/latest/admin/blockstorage-over-subscription.html) for more information relating to oversubscription for thinly-provisioned volumes.


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