[ale] backup

[Joe Bayes]

Marc Vogt typeth:

>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.

Are you trying to have 2 drives that contain exactly the same thing to
protect against the physical hardware crashing? If so, you might want
to look into the software-RAID stuff (there's an option for it when
configuring the 2.2 kernel). You want RAID level 1.

OTOH, this may be too big a flyswatter for the fairly simple job you
want to do.

If, on the other hand, you want the second disk to be time-delayed to
protect against the occasional `rm -rf /`, then one of the mirroring
options that other people have suggested would be best. 

>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 think what you meant to say was:

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

I don't know where the "i" came from in there. 

The 'c' tells tar that it's creating an archive.
The 'f' tells tar to read/write the resulting archive to/from the
	supplied filename, instead of the default /dev/rmt8 (or
	whatever default they're using theses days). 
the '-' takes the place of the supplied filename mentioned above, and
	tells tar to read/write to stdin/stdout.
the '.' is the name of the current directory. In this case, by
	supplying the '.', you are telling tar to make an archive of
	the current directory and all its subdirectories.  
the 'x' tells tar to perform an archive extraction instead of an
	archive creation. 

--joe