---
title: Reserving PVC space for file system overhead
---

# Reserving PVC space for file system overhead {#virt-reserving-pvc-space-fs-overhead}

When you create a `DataVolume` custom resource (CR) for a virtual machine (VM) by setting the `spec.storage.volumeMode`  attribute to `Filesystem`, OpenShift Virtualization automatically accounts for file system overhead.

If you specify the storage type by using the `spec.pvc` attribute in the `DataVolume` CR, OpenShift Virtualization does not add any file system overhead and the requested size is passed directly to Kubernetes.

The default file system overhead value is 6%. For example, if you request a 10 GiB disk and the `spec.storage.volumeMode` attribute is set to `FileSystem`, Kubernetes provisions a PVC of approximately 10.6 GiB so that the VM has the full 10 GiB of space available.

**Example file system overhead for data volumes**

| Requested virtual disk size | Calculated overhead (6%) | Total PVC space provisioned |
| --- | --- | --- |
| 10 GiB | 0.6 GiB | 10.6 GiB |
| 100 GiB | 6 GiB | 106 GiB |

> [!NOTE]
> You can change the default file system overhead value by editing the `HyperConverged` CR.

## Overriding the default file system overhead value {#virt-overriding-default-fs-overhead-value_virt-reserving-pvc-space-fs-overhead}

Change the amount of persistent volume claim (PVC) space that the OpenShift Virtualization reserves for file system overhead by editing the `spec.filesystemOverhead` attribute of the `HCO` object.

**Prerequisites**

- Install the OpenShift CLI (`oc`).

**Procedure**

1. Open the `HCO` object for editing by running the following command:

   ```terminal
   $ oc edit hyperconvergeds.v1beta1.hco.kubevirt.io kubevirt-hyperconverged -n openshift-cnv
   ```
2. Edit the `spec.filesystemOverhead` fields, populating them with your chosen values:

   ```yaml
   # ...
   spec:
     filesystemOverhead:
       global: "<new_global_value>"
       storageClass:
         <storage_class_name>: "<new_value_for_this_storage_class>"
   ```

   - `spec.filesystemOverhead.global` specifies the default file system overhead percentage used for any storage classes that do not already have a set value. For example, `global: "0.07"` reserves 7% of the PVC for file system overhead.
   - `spec.filesystemOverhead.storageClass` specifies the file system overhead percentage for the specified storage class. For example, `mystorageclass: "0.04"` changes the default overhead value for PVCs in the `mystorageclass` storage class to 4%.
3. Save and exit the editor to update the `HCO` object.

**Verification**

- View the `CDIConfig` status and verify your changes by running one of the following commands:

  To generally verify changes to `CDIConfig`:

  ```terminal
  $ oc get cdiconfig -o yaml
  ```

  To view your specific changes to `CDIConfig`:

  ```terminal
  $ oc get cdiconfig -o jsonpath='{.items..status.filesystemOverhead}'
  ```