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Reserving PVC space for file system overhead

By default, the Containerized Data Importer (CDI) reserves space for file system overhead data in persistent volume claims (PVCs) that use the Filesystem volume mode. You can set the percentage that CDI reserves for this purpose globally and for specific storage classes.

How file system overhead affects space for virtual machine disks

When you add a virtual machine disk to a persistent volume claim (PVC) that uses the Filesystem volume mode, you must ensure that there is enough space on the PVC for:

  • The virtual machine disk.

  • The space that the Containerized Data Importer (CDI) reserves for file system overhead, such as metadata.

By default, CDI reserves 5.5% of the PVC space for overhead, reducing the space available for virtual machine disks by that amount.

If a different value works better for your use case, you can configure the overhead value by editing the CDI object. You can change the value globally and you can specify values for specific storage classes.

Overriding the default file system overhead value

Change the amount of persistent volume claim (PVC) space that the Containerized Data Importer (CDI) reserves for file system overhead by editing the spec.config.filesystemOverhead attribute of the CDI object.

Prerequisites

  • Install the OpenShift CLI (oc).

Procedure

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

    $ oc edit cdi

  2. Edit the spec.config.filesystemOverhead fields, populating them with your chosen values:

    ...
spec:
  config:
    filesystemOverhead:
      global: "<new_global_value>" (1)
      storageClass:
        <storage_class_name>: "<new_value_for_this_storage_class>" (2)
    1 The file system overhead percentage that CDI uses across the cluster. For example, global: "0.07" reserves 7% of the PVC for file system overhead.
    2 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 CDI object.

Verification

  • View the CDI status and verify your changes by running the following command:

    $ oc get cdi -o yaml