Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > Dead Space Reclamation—UNMAP
Guest OS or in-guest UNMAP supports both Windows and Linux VMs. There are several prerequisites that must be met to take advantage of Guest OS UNMAP. There are some differences between Windows and Linux that should be noted. They are covered in the next two sections.
The prerequisites for enabling Guest OS UNMAP include:
esxcli system settings advanced set --int-value 1 --option /VMFS3/EnableBlockDelete
The prerequisites for enabling Guest OS UNMAP include:
esxcli system settings advanced set --int-value 1 --option /VMFS3/EnableBlockDelete
While Windows automatically issues UNMAP, Linux does not do so by default. Though sg_unmap and fstrim can be issued manually to free space, a simple parameter is available on file systems to reclaim space automatically. When mounting the file system (for example, ext4), use the discard option and all deleted files cause UNMAP to be issued. Here is an example.
mount /dev/sdb1 /u02 -o discard
The following command can be issued to query the device to confirm that UNMAP is supported on a LUN:
esxcli storage core device vaai status get -d <naa>
Example output:
naa.<naa>
VAAI Plugin Name: VMW_VAAI_SYMM
ATS Status: supported
Clone Status: supported
Zero Status: supported
Delete Status: supported
A device displaying Delete Status as supported means that the device can receive SCSI UNMAP commands.