When you create a VMFS6 datastore, you can modify the default parameters for automatic space reclamation.

At the VMFS6 datastore creation time, the only available method for the space reclamation is priority. To use the fixed method, edit the space reclamation settings of the existing datastore.


  1. In the vSphere Client object navigator, browse to a host, a cluster, or a data center.
  2. From the right-click menu, select Storage > New Datastore.
  3. Follow the steps required to create a VMFS6 datastore.
  4. On the Partition configuration page, specify the space reclamation parameters.
    The parameters define granularity and the priority rate at which space reclamation operations are performed. You can also use this page to disable space reclamation for the datastore.
    Option Description
    Block size The block size on a VMFS datastore defines the maximum file size and the amount of space the file occupies. VMFS6 supports the block size of 1 MB.
    Space reclamation granularity Specify granularity for the unmap operation. Unmap granularity equals the block size, which is 1 MB.

    Storage sectors of the size smaller than 1 MB are not reclaimed.

    Space reclamation priority Select one of the following options.
    • Low (default). Use the priority method for space reclamation. Enable the unmap operation at a low priority rate.
    • None. Select this option if you want to disable the space reclamation operations for the datastore.
    Note: In the vSphere Client, the only available settings for the space reclamation priority are Low and None. To change the settings to Medium or High, use the esxcli command. See Use the ESXCLI Command to Change Space Reclamation Parameters.
  5. Finish the datastore creation process.


After you enable space reclamation, the VMFS6 datastore can start releasing the blocks of unused space only when it has at least one open file. This condition can be fulfilled when, for example, you power on one of the VMs on the datastore.