Why is the used space of a LUN not consistent between VMware and QES?
VMware vSphere 5.0 introduced a new feature called Thin Provisioning Block Space Reclamation (VAAI UNMAP). This feature enables VMware ESXi to tell a storage server, such as a QES NAS, that a virtual machine (VM) has been migrated or deleted. The server can then reclaim the storage space previously occupied by the VM.
UNMAP was disabled by default in ESXi500-201112001 (ESXi 5.0 Patch 02), and then enabled again in ESXi 6.5. If UNMAP is disabled, space that can be reclaimed will be counted as free space by VMware, but as used space by QES.
If you are using VMware ESXi 5.x or 6.0 and UNMAP is disabled, you can perform space reclamation manually by running a command. For more information, see https://kb.vmware.com/s/article/2014849.