[CentOS] imaging a drive with dd

Fri Mar 3 03:57:51 UTC 2017
Robert Moskowitz <rgm at htt-consult.com>

On 03/02/2017 10:02 PM, Fred Smith wrote:
> 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.

Kind of wondered about that.

So the blocks reported by fdisk is what I should use as the count, as 
that matches the drive's real block size?