Reclaiming Space with SCSI Unmap

vSAN 6.7 Update 1 and later supports SCSI UNMAP commands that enable you to reclaim storage space that is mapped to a deleted vSAN object.

Deleting or removing files frees space within the file system. This free space is mapped to a storage device until the file system releases or unmaps it. vSAN supports reclamation of free space, which is also called the unmap operation. You can free storage space in the vSAN datastore when you delete or migrate a VM, consolidate a snapshot, and so on.

Reclaiming storage space can provide higher host-to-flash I/O throughput and improve flash endurance.

vSAN also supports the SCSI UNMAP commands issued directly from a guest operating system to reclaim storage space. vSAN supports offline unmaps as well as inline unmaps. On Linux OS, offline unmaps are performed with the fstrim(8) command, and inline unmaps are performed when the mount -o discard command is used. On Windows OS, NTFS performs inline unmaps by default.

Unmap capability is disabled by default. To enable unmap on a vSAN cluster, use the following RVC command: vsan.unmap_support –enable

When you enable unmap on a vSAN cluster, you must power off and then power on all VMs. VMs must use virtual hardware version 13 or above to perform unmap operations.