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Re: checking integrity of already written CD/DVD



In <20090331075641.GB18916@fantomas.sk>, Matus UHLAR - fantomas wrote:
>> On 29.03.09 16:27, Boyd Stephen Smith Jr. wrote:
>> > Not in my experience.  Both DVDs and CDs have a physical sector size. If
>> > the image is not a multiple of that sector size, the md5sum of the block
>> > device and the image will differ, because of the extra bits in the last
>> > physical sector.
>
>On 31.03.09 09:53, Matus UHLAR - fantomas wrote:
>> afaik, if the same image is written to multiple CDs/DVDs, they all should
>> have the same md5sum, independently on its size. That is the one md5sum
>> shjould report. The same for sha1sum.

While this may be true, the comparison asked about (and that I normally do) is 
between an ISO file and a physical DVD.  ISO files is want to burn generally 
have not been produced by dd'ing a physical DVD, so they may not take into 
account the physical limitations on the medium.

I would love it if 'md5sum /path/to/iso /dev/dvd' gave two lines with the same 
sum.  It does not usually happen that way, here.  I have to trim the /dev/dvd 
device to have exactly the same byte count as the iso file first.

>... could this problem come out of fact that there was something different
>burned on those medias before?

No, my experience is mainly with WORM optical media.
-- 
Boyd Stephen Smith Jr.                   ,= ,-_-. =.
bss@iguanasuicide.net                   ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy         `-'(. .)`-'
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