How can I speed up SD card writing speed (using /dev/disk*) on a MacBook Pro?
Just ran into the same problem and it seems to be that /dev/disk* is slow because it is buffered. If you use the corresponding rdisk device (ex: /dev/rdisk1s1) you should get the speed you expect. This is apparently a BSD thing.

Example:

% sudo dd if=pi.bin of=/dev/disk1 bs=1m count=4095
^C408+0 records in
407+0 records out
426770432 bytes transferred in 1393.452305 secs (306268 bytes/sec)

% sudo dd if=pi.bin of=/dev/rdisk1 bs=1m count=4095
4095+0 records in
4095+0 records out
4293918720 bytes transferred in 378.669512 secs (11339489 bytes/sec)


Ref:


Note on Dev Entry Access
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