Hello folks, I want to make FULL BackUp on my Mail Server but its almost 20GB of files ....., Thats why I want to make the backup on TAR files in pieces of 4.7GB to write them to DVDs.
Does any one knows a way to do that? Software or .....?
Thanks.

You could make one large tar and then split it using the split command

Look in the tar info manual in section, "9.6.1 Archives Longer than One Tape or Disk". Use the -M and --tape-length options to create multi-volume archives of a certain size. Using "split" you have to cat the files together before extracting the files. If the files are stored on disk then you could pipe the output of cat to tar, but cat'ing from multiple DVDs directly you would probably need to create a fifo file and in one shell, cat each segment in turn from the DVD file to the FIFO file, and in another console, get the input of tar from the same FIFO file.

Using a multi-volume archive would be easier and less error prone. For example, suppose a scratch ruined one of the dvd's. Each multi-volume file is a standalone archive that you can extract files from. One exception is if a very large file spans multiple volumes.

Thanks, I will try it

I take back the fifo idea. I though that further reads would be blocked until the end of the archive, but I was wrong.
(I tested the idea after my post)

You could create a separate fifo file for each disk, let's say fifo-disk1, fifo-disk2, ... fifo-disk5, for example.
Then in one shell, enter
cat fifo-disk? | tar xf -

In another shell cat each backup slice into the respective fifo file:
cat /media/dvd/backup-Aug10-2008.a >disk1
load in the next disk after it's done and enter
cat /media/dvd/backup-Aug10-2008.b >disk2

This obviously isn't so easy so using Multivolume tar backups would be the way to go.

Another alternative is to use the dar program instead. It is similar to tar but is written with backing up to discs instead. There is also a kde front end program called kdar that can make using it easier. You could set up a backup in kdar and then export the bash command. This can make it easier to automate backups in a cron job. For example, you could backup to a network share or a large enough directory. The job will create slices the size you want which you can burn to DVDs at your convenience. Or you could create one slice at a time if you run dar or kdar manually and burn each slice onto a DVD before resuming.

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I did test multiple fifo's. I created a tar backup of my ~/downloads/ directory. Then I used "split -b 10M backup.tar" which created a number of files: xaa, xab ... xai. I could have used better options for split to preserve the basename of the backup. Then I created the fifo files: for file in xa?; do fifo fifo-$file; done

Next I opened another tab in konsole and ran "cat fifo-xa? | tar -tf -"

Then one at a time I cat'ed each segment into the respective fifo file:
cat xaa >fifo-xaa
cat xab >fifo-xab
...
cat xai >fifo-xai

The output of tar would be pause between each cat command.

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Sorry for posting so much about a technique that I am not recommending, but I was curious how restoring slices of a tar archive file from DVDs could be done directly from the DVD.

Thank you jschiwal thats very helpful..., I backup my server too, later.
Thanks again.

Your welcome. It gave me an opportunity to test how to restore from DVD's containing slices of a backup. Not being able to use a single fifo file to do it wasn't what I expected, so I learned something as well.