[nflug] Verifying a cdrom image backup

[Joe]

I'm making image backups of my system in chunks that fit on cdroms.

I created files such as rootu001.iso, rootu002.iso, etc. using dump with
an unmounted file system.
Then, I used cdrecord to burn a CD which has a file called rootu001 ...
on it.
Next, I ran md5sum against each and they do not match.
I did this twice (two cdroms).
I did an ls -l of both files and the .iso file is somewhat larger than
the one on the cdrom.  There were no error messages, etc. during the
burn (using burnfree which is supported on the drive).  As far as I
know, the cdrom drive is working fine.

I just ran a 15 cdrom backup that worked fine, but I realized afterwards
that since the root file system was mounted, the backup was probably
useless, so I recreated it using a livecd with the root unmounted. 
That's the one I'm having trouble verifying now.

Am I doing something wrong?

How do I verify that what I wrote to the cdrom is identical to the image
on disk and is completely readable - a reliable/restorable copy?

TIA

Joe