I have 27GB of files that I'm trying to back up using tar and my DVD
writer.
I am able to do this by creating the tar volumes in my home directory
then burning them aftwerwards. I'm using the following command to create
the tar volumes:
tar -L 3906000 -cpMf backup.tar dirtobackup

Doing it this way allows me to divide the tarball into several similar
sized chunks and fit them on dvd's but the disadvantages are that I have
to type a new name for each tar chunk and these chunks take up space in
my home directory. I also then have to issue another command to burn
them:
growisofs -Z /dev/cdrom=backup.tar
This makes restoration a pain since I then must either copy the burned
volumes, naming them exactly as previously specified during tar creation
or I must create symlinks to /dev/cdrom named exactly as the volumes are
named.

What I trying to do is write the tar volumes directly to my DVD writer
using the following command:
tar -L 3906000 -cpMf /dev/cdrom dirtobackup

When I do this I get the following error:
tar: /dev/cdrom: Cannot open: Read-only file system

I've seen numerous examples of people writing directly to tape and
floppy drives using tar by supplying the device node name for the file
option.
I'm wondering why this method is isn't working for my DVD writer and
what my options are.