Hi TimmyT,
LUNs with thick-provisioned volumes - space reservation is enabled.
Refer - https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-vsmg%2FGUID-226B1E60-4ACF-4A63-9AE5-09E8605D53A2.html
LUNs with thin-provisioned volumes - space reservation is disabled.
Refer - https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-vsmg%2FGUID-261F894C-F3E5-4D0F-ADF6-E5E4A5F65970.html&cp=17_3_10_2
Also, be noted that ONTAP supports T10 SCSI thin-provisioned LUNs as well as NetApp thin-provisioned LUNs. T10 SCSI thin provisioning enables host applications to support SCSI features including LUN space reclamation and LUN space monitoring capabilities for blocks environments. T10 SCSI thin provisioning must be supported by your SCSI host software.
You use the ONTAP space-allocation setting to enable/disable support for the T10 thin provisioning on a LUN. You use the ONTAP space-allocation enable setting to enable T10 SCSI thin provisioning on a LUN.
The [-space-allocation {enabled|disabled}] command in the ONTAP Command Reference Manual has more information to enable/disable support for the T10 thin provisioning and to enable T10 SCSI thin provisioning on a LUN.