Fwd: strange strange problem! (please help!!)

[James Wilkinson]

David Hoffman wrote:
> I'm honestly not sure how you would find out. I am guessing about this
> theory, but here's what I'm thinking. Your original filespace...
> "/usr/local/me" could theoretically contain a symlink. Let's say for
> example, there is a symlink called "data" that points to some space on
> a different filesystem.
> 
> Then when you run your du -sm on /usr/local/me, it might not tell you
> the REAL space used if you were to copy, but instead only count
> several bytes for the symlink.

For completeness, the other option is sparse files.

When Unix (or a compatible system like Fedora) is asked to create a file
which has huge amounts of (binary) zero in it, it can be set to just
record the fact that most of the file is zero, and store those blocks
which aren't all zero. This is a sparse file.

This is under application control: it has to write the file the right
way.

For example,

[james at howells scratch]$ du -k sparse
488     sparse
[james at howells scratch]$ ls -lk sparse
-rw-rw-r--  1 james james 500000 Jan 22 20:08 sparse

a file that takes 488K on disk, but is actually 500MB (ish) large.

When you copy a sparse file with some utilities, they will write out a
non-sparse file that really does have 500 MB (or whatever) of zeros, and
takes up 500MB of disk space.

The Original Poster may want to investigate this web page:
http://rimuhosting.com/howto/rsync.jsp

James.

-- 
James Wilkinson       | "!" sez I.  And "?".  After a few speechless seconds
Exeter    Devon    UK | I come out with "%^&*".  Unless I come up with
E-mail address: james | something plausible soon I'm going to run out of
@westexe.demon.co.uk  | special characters.  -- Ben at lspace.org