AIX 3.1 File system mystery

[Warren Jones]

I've observed something very mysterious in our RS/6000 file system:
"ls -l" shows a file of ~24 Mbytes, but "du" shows the directory
using only ~17 Mbytes.  Can anyone out there offer an explanation?
The following script file tells the whole story:

|   Script command is started on Fri May 17 14:37:51 1991
| 
|   [58] ls -l /usr/tmp
|   total 17372
|   -rw-r--r--   1 sharp    macro     222048 May 17 14:34 CpGUmYQAAA
|   -rw-r--r--   1 sharp    macro     300024 May 17 14:34 CpGUmYQAAB
|   -rw-r--r--   1 sharp    macro      19052 May 17 14:35 CpGUmYQAAC
|   -rw-r--r--   1 sharp    macro          0 May 17 14:34 CpGUmYQAAD
|   -rw-r--r--   1 sharp    macro    24480468 May 17 14:36 CpGUmYQAAE !!!
|   drwxr-xr-x   2 root     system       512 Mar 09 14:06 X11
|   -rw-r--r--   1 jones    support        0 May 17 14:37 typescript
|   [59] du -s /usr/tmp
|   17376   /usr/tmp      !!!

The files "Cp*" are scratch files created by a Fortran application,
which was still running when this typescript was made.  The files
are presumably still open.

To compound the mystery:  Before the 24 Mbyte file was created
in /usr/tmp, "df" shows only ~19 Mbytes available on the /usr
partition.  Where did the extra ~7 Mbytes go?  Has IBM invented
a hyperspace extension to the JFS?

Oh, by the way, we're running AIX 3.1 (3003 update).
Thanks in advance for any enlightening comments.

Warren Jones
wjones at nwnexus.wa.com