copying /dev/da0 with dd(1) to file: output differs

[Matthias Apitz]

El día Friday, November 19, 2010 a las 12:39:13PM -0700, Warren Block escribió:

> > Just an idea: The USB key in question was new and I only created the
> > file system on it the usual way (fdisk, bsdlabel, newfs). Then I
> > restored the dump on it (which took 26 hours for 3.1 GByte dump file).
> > The USB key boots fine, btw.
> 
> 26 *hours*?  USB 1.1?

I don't think so. It is the Acer One D250 netbook.

> Well, they could be anything.  But the original filesystem has 
> formerly-used blocks with old data from deleted files.  dump doesn't 
> copy those, but dd does.
> 
> > Should I overwrite the full USB key from /dev/zero?
> 
> Possibly there would still be differences.  Filesystem metadata like 
> date last mounted, for example.  If you want a block-by-block duplicate, 
> the brute-force method is to just dd the whole drive.  Use bs=64k or 
> bs=1m to help reduce overhead.

Warren, perhaps you missed my point. I have a prepared boot-able key and
I want to give away a copy of it as a file on DVD. So I dd(1)'ed the key
to disk and did this twice to ensure that the copy was fine, but the two
files differ. How can I make sure that the file on disk (or DVD) is a
exact copy of the key?

	matthias
-- 
Matthias Apitz
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