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From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: hard disk bug
Message-ID: <823@atari.UUCP>
Date: Thu, 27-Aug-87 13:37:00 EDT
Article-I.D.: atari.823
Posted: Thu Aug 27 13:37:00 1987
Date-Received: Sun, 30-Aug-87 05:10:24 EDT
References: <385@nikhefh.UUCP>
Organization: Atari Corp., Sunnyvale CA
Lines: 39

in article <385@nikhefh.UUCP>, t19@nikhefh.UUCP (Geert J v Oldenborgh) says:
> 
> 
> Yet another weird effect.  One of the partitions on our hard disk 
> suddenly appeared full, "df" and the desktop "show info" gave 5.99 out 
> of 6 Mb used.  "du", however, only found 3.5 Mb to be accounted for (du 
> does not count directories, so a small discrepancy is to be expected).  
> We next moved all of the files on this partition to another one.  2.5 Mb 
> was still occupied...   [...]

The obvious answer is that at some time (or at several times), files
were created, written to, but not closed.  This only happens if your
system is reset or powered off, because when a process terminates, all
its files are closed automatically.  But if this does happen, the
clusters allocated to the file in question will be marked as "used" in
the FAT, but won't be linked with any directory entry.  These are known
as "lost clusters," and CHKDISK would find them, if we had one.  We do
have one in-house, but I don't know a release date or anything.  If "du"
looks at files rather than the FAT, it would miss these, too. 

Here's another possibility:

Each cluster in a subdirectory can hold 32 files.  When you delete a
file, that entry is marked as "available," and the next file creation
will use it.  If there are no available entries, GEMDOS will allocate
another cluster to that subdirectory.  Under no circumstances will
GEMDOS de-allocate a cluster for a subdirectory -- even if all the
entries in it are for deleted files.  This means that if your
application uses lots of files in subdirectories, and you delete all the
files (but not the subdirectories themselves), there will still be lots
of clusters allocated to the subdirectories. 

If you actually remove the subdirectories, of course, the disk space
allocated to them is freed. 

/----------------------------------------------\
| Opinions expressed above do not necessarily  |  -- Allan Pratt, Atari Corp.
| reflect those of Atari Corp. or anyone else. |     ...lll-lcc!atari!apratt
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