The filesystem resides inside the volume.  As you already noticed, there is a small overhead between volume (1000000) and filesystem (984741), typically less than 2 %  1008374984 is about the size of the FS in KB (984741 * 1024 = 1008374,784 KB)
Hi,  can anyone tell me what the last field in the SizeValues means:   $ nas_fs -size UCS-FS total = 984741 avail = 862691 used = 122050 ( 12% ) (sizes in MB) ( blockcount = 2048000000 ) volume: total = 1000000 (sizes in MB) ( blockcount = 2048000000 ) avail = 862691 used = 137309 ( 14% )   And what's the difference between volume total(1000000) size and total size (984741)  Regards, John 
nas_fs -query SizeValues fields