VM Deployment Failed Due to Insufficient Storage

Problem

VM deployment using Ephemeral storage fails with "No valid host was found" on ostackhost logs, and "insufficient resources or a temporary occurrence as compute nodes start up" error in Nova-scheduler logs.

INFO nova.scheduler.manager [None [Req-UUID] [Project-ID] [User-ID] - - default default] Got no allocation candidates from the Placement API. This could be due to insufficient resources or a temporary occurrence as compute nodes start up.

Environment

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

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

Cause

VM deployment failed because the requested size surpassed the resource provider's max_unit allocation. Further details on [max_units] allocation.

Diagnostics

On underlying host:

1. Get the VM disk storage path using command given below:

$ sudo virsh domblklist <VM_UUID>

$ sudo virsh domblklist <VM_UUID>
 Target   Source
-------------------------------------------------------------------------
 vda      _opt_data_instances_[VM_UUID]_disk

1. Check where the VM disk storage path is mounted.

The OpenStack placement API takes Disk dev mapper size into account when calculating the resource provider's max unit value.

$ df -lh _opt_data_instances_<VM_UUID>_disk

$ sudo df -lh _opt_data_instances_[VM_UUID]_disk
Filesystem                         Size  Used Avail Use% Mounted on
[Disk dev mapper path]             98G   69G   25G  74% _

Here,

• VM disk storage path is mounted on "/".

• The OpenStack consider this 98 GB size while calculating the resource provider's max unit value.

OpenStack CLI:

1. List down all available resource providers. These resource providers are responsible for allocating the CPU, Memory and Storage to the VMs.

$ openstack resource provider list

1. Check for max_unit for Disk_GB on all resource providers listed above.

Any VM requesting an ephemeral storage disk above the max_unit value will fail with "insufficient resources or a temporary occurrence as compute nodes start up" error in the nova-scheduler logs.

$ openstack resource provider inventory list <RESOURCE_PROVIDER_UUID>

$ openstack resource provider inventory list <RESOURCE_PROVIDER_UUID>
+----------------+------------------+----------+----------+----------+-----------+--------+-------+
| resource_class | allocation_ratio | min_unit | max_unit | reserved | step_size |  total |  used |
+----------------+------------------+----------+----------+----------+-----------+--------+-------+
| VCPU           |             16.0 |        1 |       80 |        0 |         1 |     80 |     6 |
| MEMORY_MB      |              1.5 |        1 |   773663 |      512 |         1 | 773663 | 12288 |
| DISK_GB        |           9999.0 |        1 |       97 |        0 |         1 |     97 |   120 | 
+----------------+------------------+----------+----------+----------+-----------+--------+-------+

Here,

The DISK_GB for the resource provider is 97GB, a value determined by the VM's disk storage configured for the root (/) mount point.

Resolution

1. Use image which has storage requirements less than the max_unit value from all available resource providers.

2. It is recommended to use Cinder-backed volumes for VM deployments.

Validation

1. How much storage is requested by the image used to deploy VM.

$ openstack image list --all | grep -i <IMAAGE_USED_BY_VM>
$ openstack image show <IMAGE_UUID> --fit

+------------------+-----------------------------------------------------------------------+
| Field            | Value                                                                 |
+------------------+-----------------------------------------------------------------------+
...                .                                                                       .
| disk_format      | qcow2                                                                 |
| file             | _v2_images_[image_uuid]_file                                          |
| id               | [image_uuid]                                                          |
| min_disk         | 80            <----- Image requires 80 GB disk, within max_unit value |
| min_ram          | 0                                                                     |
| name             | [image_name]                                                          |
...                .                                                                       .
+------------------+-----------------------------------------------------------------------+

1. If these steps prove insufficient to resolve the issue, reach out to the Platform9 Support Team for additional assistance.