can ext3 directory entries be overwritten? -- Re: extremely slow "ls" on a cleared fatty ext3 directory on FC4/5

[Theodore Tso]

On Sun, Aug 13, 2006 at 11:57:41AM -0700, Robinson Tiemuqinke wrote:
> Hi, all,
> 
>  I'm a newbie to ext3 file system, but what a pity if
> ext3 could not shrink after containing files and
> subdirectories get deleted.
> 
>  If the ext3 directory could not shrink, then another
> natural question is: can the deleted directory entries
> be overwritten by new files/subdirs? The following is
> an example to detail my question:

Yes, of course.  If a directory contains deleted directory entries,
they do o fcourse get reused.  So in the case where the number of
files remains more or less at a steady state, ext3 will do fine.  What
ext3 does not currently handle is the case where someone creates 131
megabytes worth of directories (which is enough for 4-8 million
files!), and then deletes them all.  The directory will not shrink
back down to its original size.

Likewise, most modern filesystems implement on-line resizing, where
the total size of the filesystem can be extended if you are using an
LVM and/or RAID system, and can expand the underlying
volume/partition.  However, no filesystems that I know of implement an
on-link shrink operation.  Some have an off-line shrink operations;
some don't even have that.

						- Ted