Hi,

I am trying to backup some of my data by tarring in to another hard drive (I am in fact compressing them using bzip2 later -- but that's not relevent to this question).

My original directory tree has taken (du -sk <directory>) about 1.9GB. So, I was surprised to see that the tar file has taken 3.3GB.

Command used was find <source directory> |tar -cv <tar file> -T -

Since this is a small part of a Huge backup program, if things behave this way, I am going to be in trouble.

Can somebody help me to figure out what is happening.

Thanks in advance

The only thing I could think of it that you've got a core file somewhere, that hasn't been noticed for whatever reason. Try searching for a file named "core" (find / -name core) they're usually massive (about 1.5GB) and they can safely be deleted.
Otherwise that is very strange.
Guy

Try a much simpler command such as:
tar zcvf /path/to/backup.tgz /directory/to/backup