Using dd to Make a Clone of a Drive

Giorgos Keramidas keramida at
Thu Feb 9 14:02:45 PST 2006

On 2006-02-09 14:36, Martin McCormick <martin at> wrote:
> 	After installing FreeBSD5.4, the ISC dhcp server and ISC bind
> on a hard drive, I wanted to clone that drive to a second drive so as
> to generate a second server, using what I had already installed as a
> template.  I used the following command:
> dd if=/dev/da0 of=/dev/da1 bs=512
> 	It turns out that dd defaults to 512-byte blocks so I didn't
> really need the bs=512, but I am not sure I haven't made some other
> type of mistake.  The dd command has been running for about 4 hours on
> a very fast system, with a 1-gig processor, 1 gig of RAM and two 31-GB
> drives.  One would think it should have finished by now, but it is
> still running.  Is this a valid method of copying the entire contents
> of one drive to another?  Thank you.

Bah!  That's too slow for my taste.  I would usually go for a newfs,
dump, and restore option.  For instance, to create a copy of /usr on a
second disk:

    newfs -U /dev/ad1s1a
    mount /dev/ad1s1a /mnt
    dump -0 -a -L /usr | ( cd /mnt ; restore ruvf - )

Copying with dd(1) is not as fast :)

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