Backing up to DVDs

Sam Couter sam at
Fri Nov 8 08:12:51 EST 2002

Michael James <michael at> wrote:
> Has anyone built a system around them?
> Say fortnightly full backup/archives to DVD
>  and incrementals to rewriteable CDs?

I've just hacked up some quick scripts that use rsync to copy data from
all the machines I want to backup, afio to create archives of that
stuff, then burn the archives to CD-R. Incremental or differential
backups are on the TODO list, as is the ability to handle more than one
CD worth of data.

> Of course (if I'd thought about it) everything turns out unwriteable,
>  but also everything turns out readable, even shadow etc.

Use your favourite archive format. That's what they're designed for.

> Or could I? How about burning the ISO as a file.
> Then mount it instead of the disk?

Create a filesystem that can handle the permissions and so on that you
want (perhaps ext2?) and burn *that* as a file. Mount the CD, then mount
the file using loopback.

Won't work on non-Linux systems.

> Well what about tar then,
>  no theoretical reason I can't "mount -t tarfs /cdrom/ /mnt/"

Sure, if you write the driver for tarfs. :)

It'd be easier to use an existing filesystem format and mount it using
the loopback device under Linux. For space saving ability, compress the
CD image and use the transparent decompression support in the
2.4.something kernels.

> PS: I have long thought that the function of a backup system
>      (what's changed and keep me a copy)
>      is very close to the function of an intrusion detection system,
>      (what's changed and should I be worried)
>      and the guts of the most elegant approach are already written in rsync.
>     But then I've always been an rsync fan.

The recommendation for IDS is to burn the checksum database and whatever
else you need to boot to a CD, and to boot off that CD when you want to
do your integrity check. The biggest difference here is that for IDS you
only need a one-way hash value generated from each interesting file
(which doesn't take much space). For a backup, you need to be able to
reconstruct the entire file itself.
Sam "Eddie" Couter  |  mailto:sam at
Debian Developer    |  mailto:eddie at
                    |  jabber:sam at
OpenPGP fingerprint:  A46B 9BB5 3148 7BEA 1F05  5BD5 8530 03AE DE89 C75C
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