>  > I used a 75 GB target file on a ~ 108 GB /usr partition and ls -l
>>  /usr confirms it is 75 GB in size.  However, df says /usr has 59 GB
>>  available, which doesn't add up.
>
>What does 'ls -ls' show, the file could be sparse

That must be it, thanks David.

# ls -ls /usr
total 33269954
        2 drwxr-xr-x   3 root  wheel          512 Mar  4 18:39 CVS
        2 drwxr-xr-x   2 root  wheel         1024 Feb 27 18:31 INSTALL
        2 drwxr-xr-x   8 root  wheel          512 Feb 25 00:23 X11R6
        8 drwxr-xr-x   2 root  wheel         7168 Feb 27 18:28 bin
        2 drwxr-xr-x   3 root  wheel         1024 Feb 27 18:27 games
        2 drwxr-xr-x   3 root  wheel          512 Feb 27 18:32 home
        4 drwxr-xr-x  46 root  wheel         3584 Feb 27 18:27 include
33269904 -rw-r--r--   1 root  wheel  80530636801 Mar  3 17:30 iscsi-target0
       10 drwxr-xr-x   4 root  wheel         9216 Feb 27 18:27 lib
        2 drwxr-xr-x   4 root  wheel          512 Feb 25 00:23 libdata
        2 drwxr-xr-x   8 root  wheel         1024 Feb 27 18:28 libexec
        2 drwxr-xr-x   2 root  wheel         1024 Feb 25 01:24 lkm
        2 drwxr-xr-x   2 root  wheel         1024 Feb 25 01:23 mdec
        2 drwxrwxr-x  52 ray   wheel         1024 Mar  2 17:03 pkgsrc
        6 drwxr-xr-x   2 root  wheel         4608 Feb 27 18:27 sbin
        2 drwxr-xr-x  28 root  wheel          512 Feb 25 00:23 share
#


After copying another 18 GB or so of files to the target:

# ls -ls /usr
total 47436404
        2 drwxr-xr-x   3 root  wheel          512 Mar  4 18:39 CVS
        2 drwxr-xr-x   2 root  wheel         1024 Feb 27 18:31 INSTALL
        2 drwxr-xr-x   8 root  wheel          512 Feb 25 00:23 X11R6
        8 drwxr-xr-x   2 root  wheel         7168 Feb 27 18:28 bin
        2 drwxr-xr-x   3 root  wheel         1024 Feb 27 18:27 games
        2 drwxr-xr-x   3 root  wheel          512 Feb 27 18:32 home
        4 drwxr-xr-x  46 root  wheel         3584 Feb 27 18:27 include
47436352 -rw-r--r--   1 root  wheel  80530636801 Mar  4 20:35 iscsi-target0
       10 drwxr-xr-x   4 root  wheel         9216 Feb 27 18:27 lib
        2 drwxr-xr-x   4 root  wheel          512 Feb 25 00:23 libdata
        2 drwxr-xr-x   8 root  wheel         1024 Feb 27 18:28 libexec
        2 drwxr-xr-x   2 root  wheel         1024 Feb 25 01:24 lkm
        2 drwxr-xr-x   2 root  wheel         1024 Feb 25 01:23 mdec
        2 drwxr-xr-x  14 root  wheel          512 Mar  4 19:09 pkg
        2 drwxrwxr-x  52 ray   wheel         1024 Mar  2 17:03 pkgsrc
        6 drwxr-xr-x   2 root  wheel         4608 Feb 27 18:27 sbin
        2 drwxr-xr-x  28 root  wheel          512 Feb 25 00:23 share
#