[ale] backup

[Marc Vogt]

I have two 18 Gig drives and I would like to temporarily use 
one of them as a backup of the other, so that it is an exact copy
not just all the stuff in .tar files.  One drive is mounted as 
/home/group and the other as /home/group2.

I thought of just simply:

cp -R /home/group /home/group2/

but then /home/group2/ will accumulate files that have been deleted
between "backups".  

or I could 

cd /home/group2; rm -fr *; cp -R /home/group /home/group2/

this solves the above problem, but has the problem that no backup
of most or all files exists after the rm.


Any better ideas?  I'm sure this isn't an uncommon thing to want to do,
so any ideas would be appreciated.  Should I use dd?  If so, how?
I can't seem to get it to work.  

Also the man page I have for tar says:

 Use tar in a pipeline to copy the entire file system hierarchy under
      fromdir to todir:

   cd fromdir ; tar cf - . | ( cd todir ; tar xf -i )


well, that would be cool if it worked.  It says that -i is not a file!

I did:

   cd /home/group ; tar cf - . | ( cd /home/group ; tar xf -i )

also I am not unfamiliar with tar and this makes no sense to me.
tar -cf .   ????????????

If you have the -f option you need to name a file that will be the tar 
bundle and then after that tell it what goes in the tar bundle (the .
could be appropriate here.)  I guess it (as written) is supposed
to put tar . and pipe it directly to another tar instead of writing
to a file, which would be great if it worked, but it doesn't.
Can anyone help me with either this syntax or a better way to do this.



thanks

Marc



p.s.  I never get copies of email that I send to ale, although I get 
other people's.  I wonder if you all are getting them.