Pls Help: Backups using XP Pro and DVD-RW drive

I want to do weekly manual drag and drop backups to my DVD-RW drive (using
XP Pro).

Question: Do I have to reformat my DVD-RW disc each time I want to do new
backups or can I simply put my DVD-RW disc in the drive and drag new
files/write them?

I seem to be having trouble appending data to an existing DVD-RW disc. It
won't let me append to a disc unless I reformat it and write it over again.
Is this the nature of the technology?

Thanks.


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