[nflug] Verifying a cdrom image backup

[Brad Bartram]

My first comment would be to detail how you did each step in your process.
Especially what you were trying to hash and the command used.

In lieu of that, my first step would be to copy the data from the cd onto
your hard drive in a directory, assuming the iso file, as a file, is on cd -
and then hashing it once it's back on your hard drive.  Depending on your
method of burning, as well as other various things, it's very possible and
likely to get differing hash values but still not alter anything
substantial.

The best method, hands down, is to test your restore.  This is a critical
step in any backup plan.  Don't rely on concept and best practices or logic
- actually try it out and see what breaks.

So - aside from all of my sidestepping and pontificating above - here is
what I would do:

Look at the original iso files and hash them.  Look at the cd and hash the
files on cd - make sure you don't hash the device itself as that will give a
different value.  If the hashes are different, then copy the files back from
cd and hash them.  Then try mounting the iso files themselves.  Check to
make sure things look alright and are valid.  If things are all messed up
and your iso won't mount - then start over again from concept and work
forward.

Brad

On Fri, Dec 12, 2008 at 2:39 AM, Joe <josephj at main.nc.us> wrote:

> 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
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