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 >