Re: DVD fails "verify" but copies just fine

isw <isw@xxxxxxxxxxx> wrote:

I stuck a Memorex DVD burner in my Blue & White Mac a couple of weeks
ago. After a couple of successfully verified burns (two out of three,
actually), I have made sixteen coasters in a row -- all of them had a
failure to verify, but not at the same place on the DVD every time.

It's an idiot failing of the burn programs that they

1) stop after the first verify failure, so there's no way to tell how
many errors actually exist

2) do not tell you the name of the file(s) with the error -- just in
case you don't care

So after trying to come up with a way to compare some 4 Gig worth of
files (the source vs. the "failed" DVD), I finally thought of something:
I just stuck the DVD in the slot and dragged everything over to a hard
drive -- I figured that when the defective file came up, I'd get an
alert, and I would know which one it was.

No such luck; the entire batch of files was copied just fine.

So what's going on here? Could it be that the burn was OK but the verify
is what's failing?

What does a "verify" do, exactly? I don't think the source files are
actually re-read and compared to the target, but I don't really know.

Isaac

I think there is enough compartison of source and target files (a
checksum, file size, or the like) that if a file has changed between
burning and verification it will fail to verify.

Some people don't bother about verification because of this.

But I have just (internal Matshita drive on a G4 PowerBook) haf a bunch
of data disks fail verification using Toast but work successfully with
the Finder. And these did turn out to have faulty files. I used your
method of copying back, and on each disk one file failed to copy.

So I think veification is worth while, and then copying back if
verifcation fails,so as to check if some copied files are bad.
--
http://www.decohen.com
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