[CentOS] Solved Re: imaging a drive with dd

[Robert Moskowitz]

The following worked:

# dd if=/dev/sdb of=cubietruck.img bs=512 count=6268927

6268927+0 records in
6268927+0 records out
3209690624 bytes (3.2 GB, 3.0 GiB) copied, 114.435 s, 28.0 MB/s

So bs= IS the drive blocksize.

This is the result of trying a number of different values for bs and count.

thank you


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.
>
> Fred
>