[CentOS] imaging a drive with dd

Fri Mar 3 03:02:56 UTC 2017
Fred Smith <fredex at fcshome.stoneham.ma.us>

On Thu, Mar 02, 2017 at 09:06:52PM -0500, fred roller wrote:
> On Thu, Mar 2, 2017 at 8:36 PM, Robert Moskowitz <rgm at htt-consult.com>
> wrote:
> > dd if=/dev/sdb of=os.img bs=1M count=3210
> >
> I would recommend bs=512 to keep the block sizes the same though not a huge
> diff just seems to be happier for some reason and add status=progress if
> you would like to monitor how it is doing.  Seems the command you have
> should work otherwise.

The dd blocksize has nothing to do with the disk sector size.

the disk sector size is the number of bytes in a minimal read/write
operation (because the physical drive can't manipulate anything smaller).

the dd blocksize is merely the number of bytes read/written in a
single read/write operation. (or not bytes, but K, or Kb, or other
depending on the options you use.)

It makes sense for the bs option in dd to be a multiple of the actual
disk block/sector size, but isn't even required. if you did dd with a
block size of, e.g., 27, it would still work, it'd just be stupidly slow.


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