On Mar 3, 2017, at 10:49 AM, Lamar Owen <lowen at pari.edu> wrote: > > On 03/02/2017 11:57 PM, Robert Moskowitz wrote: >> 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. > > You can set bs to a multiple of 512 and it will go a lot faster. Maybe, maybe not. OP said he’s on an embedded system, which often implies low-end eMMC or SD type storage, and 28 MB/sec is typical for such things. When mirroring HDDs and proper SSDs, yes, you want to use large block sizes.