backups & cloning

Polytropon freebsd at
Wed Sep 30 20:40:37 UTC 2009

About the dd method:

On Wed, 30 Sep 2009 11:30:58 -0400, Jerry McAllister <jerrymc at> wrote:
> It can be used, but it is not a good way to do it.

For regular backups or even for cloning, it's not very
performant, I agree. I'm mostly using this method for
forensic purposes, when I need a copy of a media (a
whole disk, one slice or a particular partition) to toy
around with, so I don't mess up the original data.

> That is because it copies sector by sector and the new 
> disk/filesystem may not match the old exactly. 

That's a known problem. Another problem is time complexity.
The dd program does copy everything - even the unused disk
blocks (which don't need to be copied). This makes this
process often last very long.

> Besides
> when it is newly written on a file by file basis, it can
> be more efficiently laid out and accomodate any changes in
> size and sector addressing.  dd cannot do that.

That's true. This is the point where tools like cpdup and
rsync come into mind (according to creating backups or

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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