Starting with vSphere 5.1, Horizon 7 creates linked-clone virtual machines in an efficient disk format that allows ESXi hosts to reclaim unused disk space in the linked clones. Upgrading pools to use this feature involves changing settings in vCenter Server, View LDAP, and pool settings and then recomposing the pool.

Note: The space reclamation feature is not supported if your virtual machine desktops are hosted on vSAN datastores or Virtual Volumes datastores.

Although the space reclamation feature reduces the amount of disk space used for a virtual machine, it can reclaim only space that is not used. This feature cannot reclaim disk space created by virtual machines that have not been optimized. To optimize an operating system image, you can turn off Windows services such as the indexer service, the defragmenter service, and restore points. For details, see the topics "Optimize Windows Guest Operating System Performance," "Optimize Windows 7 and Windows 8 Guest Operating System Performance," and "Optimizing Windows 7 and Windows 8 for Linked-Clone Desktops," in Setting Up Virtual Desktops in Horizon 7.

Important: Because this procedure involves recomposing the desktop pool, any changes that end users have made to the operating system disk will be lost.
  1. If all vCenter Server instances and ESXi hosts for the pool are not at VMware vSphere 5.1 or later, upgrade them to 5.1 or later.

    For instructions, see the VMware vSphere Upgrade Guide.

  2. If all virtual machine desktops in the pool are not VMware vSphere 5.1 (virtual hardware version 9) or later virtual machines, upgrade them.
    • In the parent virtual machine, upgrade VMware Tools to the latest VMware vSphere 5.1 or later version, and upgrade the virtual machine to the latest version, which must be virtual hardware version 9 or later.

      For instructions, see the VMware vSphere Upgrade Guide.

    • Take a snapshot of the parent virtual machine. For instructions on taking snapshots, see the vSphere Client online help.
    • Use the snapshot of the parent virtual machine you just created to recompose the desktop pool. For instructions on recomposing pools, click the Help button in Horizon Administrator.

    Recomposing the pool from a snapshot of an upgraded virtual machine is just one method of upgrading all virtual machines in a linked-clone pool. You can also upgrade the virtual machines one by one.

  3. Upgrade the disk format used for the virtual machines.
    • On the Connection Server host, use ADSIEdit to navigate to the server group that corresponds to the pool, and change the value in the pae-UseSeSparseFormat field from 0 to 1.
    • Recompose the desktop pool.
  4. Use Horizon Administrator to edit the vCenter Server settings, navigate to the Storage tab, and select Reclaim VM disk space.

    For instructions on editing server settings, click the Help button in Horizon Administrator.

  5. Use Horizon Administrator to edit the pool settings, navigate to the Advanced Storage section, select Reclaim VM disk space, and set the threshold for space reclamation to 1GB.