using dd to duplicate disks/partitions of slightly different sizes - works?

RW fbsd06 at
Sat Dec 1 18:47:00 PST 2007

On Sat, 1 Dec 2007 20:53:41 -0500
Mike Jeays <mike.jeays at> wrote:

> I tried using dd with two 80GB disks, using a much larger block size
> (512M), booting Knoppix to make sure the filesystems on the 'input'
> disk were quiescent.  It worked, but took an amazing 14 hours, which
> is only about 1.5 Mb/sec.  The 'output' drive was on an IDE connector
> shared with the CD device, so that may have been a cause of the poor
> performance.

Probably that was the cause, I've done a few:
  dd if=/dev/random of=<disc> bs=1m 

recently, and they all went an order of magnitude faster than that,
even on PATA drives.

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