See below... I'm referring to the "Occupied Size" property.
lun show -v /vol/bss_csv_hvntn_os/bss_csv_hvntn_os1/bss_csv_hvntn_os1.lun
/vol/bss_csv_hvntn_os/bss_csv_hvntn_os1/bss_csv_hvntn_os1.lun 5.9t (6487278336000) (r/w, online, mapped)
Serial#: D14Mr$CH248l
Share: none
Space Reservation: enabled
Multiprotocol Type: hyper_v
Maps: hvntn_csv=0
Occupied Size: 5.3t (5867480559616)
Creation Time: Tue Feb 19 14:43:43 CET 2013
Cluster Shared Volume Information: 0x3
lun show -v /vol/bss_csv_hvntn_os_HA/bss_csv_hvntn_os_HA_1/bss_csv_hvntn_os_HA_1.lun
/vol/bss_csv_hvntn_os_HA/bss_csv_hvntn_os_HA_1/bss_csv_hvntn_os_HA_1.lun 2.0t (2199036833280) (r/w, online, mapped)
Serial#: D14Mr$CH248r
Share: none
Space Reservation: enabled
Multiprotocol Type: hyper_v
Maps: hvntn_csv=2
Occupied Size: 1.7t (1872039890944)
Creation Time: Mon Sep 9 13:30:42 CEST 2013
Cluster Shared Volume Information: 0x3
Also System Manager shows the same:

And here's how these LUNs look (respectively) inside Windows Server:

