Windows 2012 (including R2) Hosts will by default issue SCSI "TRIM and Unmap" commands equivalent to the entire size of the Virtual Disk. This behavior is regardless if the 'Perform a quick format' option is checked. This will significantly slow down the format process.
It is possible to disable the SCSI TRIM and Unmap feature on the Host for the duration of the format.
Using a Windows CMD window on the Host issue the command:
To re-enable the feature use the following command:
To verify the current setting use the following command:
Information about this new feature can be found here.