In-Guest UNMAP in ESXi 6.x

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The discussion above speaks only about space reclamation directly on a VMFS volume. This pertains to dead space accumulated by the deletion or migration of virtual disks, ISOs or swap files (mainly). The CLI-initiated UNMAP operation does not pertain though to dead space accumulated inside of a virtual disk. Dead space accumulates inside of a virtual disk in the same way that it accumulates on a VMFS volume—deletion or movement of files.

Prior to ESXi 6.0 and virtual machine hardware version 11, guests could not leverage native UNMAP capabilities on a virtual disk because ESXi virtualized the SCSI layer and did not report UNMAP capability to the guest.

In ESXi 6.0, guests running in a virtual machine using hardware version 11 can now issue UNMAP directly to thin virtual disks. The process is as follows:

  1. A guest application or user deletes a file from a file system residing on a thin virtual disk.
  2. The guest automatically (or manually) issues UNMAP to the guest file system on the virtual disk.
  3. The virtual disk is then shrunk in accordance to the amount of space reclaimed inside of it.
  4. If EnableBlockDelete is enabled, UNMAP will then be issued to the VMFS volume for the space that previously was held by the thin virtual disk. The capacity is then reclaimed on the FlashArray.

    Currently, in-guest UNMAP support is limited to Windows 2012 R2 or Windows 8. Linux requires a newer version of SCSI support that is under consideration for future versions of ESXi.

    Prior to ESXi 6.0, the parameter EnableBlockDelete was a defunct option that was previously only functional in very early versions of ESXi 5.0 to enable or disable automated VMFS UNMAP. This option is now functional in ESXi 6.0 and has been re-purposed to allow in-guest UNMAP to be translated down to the VMFS and accordingly the SCSI volume. By default, EnableBlockDelete is disabled and can be enabled via the Web Client or CLI utilities.

    Figure 20. Enabling EnableBlockDelete in the vSphere 6.0 Web Client interface

    In-guest UNMAP support does not require this parameter to be enabled. Enabling this parameter only allows in-guest UNMAP to be translated down to the VMFS layer. For this reason, enabling this option is a best practice for ESXi 6.x and later.