fastest raw device copy?

Ivan Voras ivoras at freebsd.org
Fri Oct 31 06:15:52 PDT 2008


Jeremy Chadwick wrote:
> On Fri, Oct 31, 2008 at 09:48:16AM +0100, Christoph Kukulies wrote:

>> What would be the fastest way to do that sector by sector copy? I'm  
>> using dd right now,
>>
>> dd if=/dev/ad0 of=/dev/da0 bs=10000000

> On the flip side, your blocksize (bs) there is quite high for no good
> reason.  I'd pick something more like bs=64k or bs=128k.  The default
> (512) is too small for what you want, but 10MBytes is silly.

Not only that, but "10000000" isn't even correct - it needs to be a
multiple of sector size. Generally, using suffixes will do the right thing:

dd if=/dev/ad0 of=/dev/da0 bs=1m

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