As some of you are probably already aware, one of the storage-related features added to vSphere 5 is support for the SCSI UNMAP command. While you would normally want this functionality enabled, there could be instances where you might want to disable this functionality. Unfortunately, there’s no option in the user interface to enable or disable SCSI UNMAP support.
However, you can use
esxcli to enable or disable UNMAP support:
esxcli system advcfg setvalue --int-value [0|1] --option /VMFS3/EnableBlockDelete
Setting this value to 0 disables SCSI UNMAP support; setting the value to 1 enables it.
Many thanks to Cormac Hogan of VMware and Cody Hosterman of EMC for their help with this command.