Using dd to Make a Clone of a Drive

Mike Jeays mj001 at
Thu Feb 9 13:24:22 PST 2006

On Thu, 2006-02-09 at 14:36 -0600, Martin McCormick 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.
> Martin McCormick WB5AGZ  Stillwater, OK 
> Systems Engineer
> OSU Information Technology Department Network Operations Group
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Mike Jeays

You can use a much bigger block size, and the job will take significantly less time to run.
I have successfully used a blocksize of 512000.  Keep it to a multiple of 512.
I haven't tried even larger block sizes, but I think they would work fine.

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