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Re: Some help with dd backing up into an iso




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On Tue, Mar 07, 2017 at 10:26:25AM +0200, Teemu Likonen wrote:
> David Christensen [2017-03-06 21:05:31-08] wrote:
> 
> >     # dd if=/dev/sda | gzip > myimage.img
> 
> What's the point of using dd?
> 
>     gzip </dev/sda >myimage.img
> 
> I don't know about you but many people seem to think that dd is some
> kind of special tool [...]

> To copy a device file:
> 
>     cat /dev/foo >image.img
> 
> To write to a device:
> 
>     cp image.img /dev/foo
>     sync

Yep. That's when you want to copy all the source, whereas dd comes in
handy whin you know how much to copy. So this idiom makes sense

  dd if=/dev/zero of=lotsofnull bs=1024 count=1024 # copy 1M of zeros

whereas (kids, *don't try this at home)

  cp /dev/zero of=lotsofnull # try to fill up your hard disk

ain't what you're usually looking for ;-P

But yes dd is a dinosaur from olden times where block sizes were a
thing (although I have seen slight speed differences by varying bs
on a fairly modern system, but that might have been some voodoo).

regards
- -- tomás
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