On Wed, 19 Apr 2017 06:56:18 -0700 (PDT)
jack4747@gmail.com wrote:

> Il giorno mercoledì 19 aprile 2017 15:32:44 UTC+2, Rob Morley ha
> scritto:

> > But copying the whole disk rather than just individual files you
> > don't need to format the target drive before copying.
>
> yes, but you end up with a target that has a partition the same size
> of the source, even if the target is bigger...

That's easily fixed.  Format before, or re-size after - looks like
swings and roundabouts to me.
>
> > > Much better (and faster) in this case to mount both HDs and do a
> > > cp -a.
> >
> > I doubt there's much in it - it's possible dd will be faster
> > because of fragmentation.
>
> dd-ing will preserve fragmentation, copying will remove fragmentation.

If fragmentation is a problem in use (not normally with Linux, but
sometimes with Windows IME) you can just copy the fragmented files
once you have all that lovely extra disk space.
>
> other cons of dd is that if the copy is interrupted for some reason,
> it need to be restarted from the beginning because the target will
> not be usable until the end. With cp at least the copied files are
> usable.

They're copies - you already have the originals on the source drive,
why would you need them on the target before the transfer is complete?

> Better solution would be rsync, so if the copy is
> interrupted, it will resume without problem.
>
You can stop and resume dd quite easily - send SIGUSR1 to show
progress, then kill dd.  You resume by giving appropriate values to
skip and seek using the record count produced by SIGUSR1.
Or just send the signal occasionally and redirect output to a file so
you have a record of a fallback point if the dd encounters some
insurmountable problem like a host crashing.

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