[lug] proper way to MD5SUM a cdrom?

[Paul E Condon]

On Mon, Jun 14, 2004 at 06:49:05PM -0600, David Anselmi wrote:
> Paul E Condon wrote:
> >>>On Sat, Jun 12, 2004 at 06:39:41PM +0000, D. Stimits wrote:
> >>>
> >>>>Just a question on verifying CD-R's. I have the ISO, and have run 
> >>>>md5sum on it, it looks good. Then I burn it with cdrecord. How do I 
> >>>>verify the 
> 
> You can do md5sum /dev/cdrom (or whatever the right device is).
> 
> >Suggestion: Don't do an MD5SUM check. Instead, read the whole CD with:
> >dd if=/dev/scd8 of=cpybak
> >and then use 
> >cmp cpybak original.iso
> >to check byte by byte the copy against the original
> 
> Why do you say that?  Hmm, probably cmp is faster than md5sum but:
> 
> cmp original.iso /dev/cdrom
> 
> should be faster than recopying the CD, don't you think?
> 

Actually the time spent on cmp disk to disk, is trivially small
compared the time to copy. Stimits is not the only one who has worried
about block size differences between HD and CD. dd restores the CD
image to the same blocking as the iso from which it was
made. Different block sizes may be only an emotional issue, but my way
avoids the worry. The real point of my suggestion is that MD5SUM is only
useful for situations in which the source and destination are separated
by a relatively narrow band channel, such as download from the internet.

Peace.

-- 
Paul E Condon           
pecondon at mesanetworks.net