Dear community,
I wanted to drop my 2 cents here by reporting results.
bmap-tools is indeed faster.
Please proceed with the repo indicated or in ubuntu:
sudo apt-get install bmap-tools
Make sure that your device is connected and present in the /dev partition and both files, the raw image and the .bmap file are in the same folder.
I tested with a RaspberryPi3, and after .rpi-boot it is necessary to umount any existing partitions except for /dev/sdb (in my case)
Then proceed:
mvargasevans@X1:~//mender-builder$ sudo bmaptool copy ./development.rpi-sdimg /dev/sdb
bmaptool: info: discovered bmap file './development.rpi-sdimg.bmap'
bmaptool: info: block map format version 2.0
bmaptool: info: 1661952 blocks of size 4096 (6.3 GiB), mapped 606924 blocks (2.3 GiB or 36.5%)
bmaptool: info: copying image 'development.rpi-sdimg' to block device '/dev/sdb' using bmap file 'development.rpi-sdimg.bmap'
bmaptool: WARNING: failed to enable I/O optimization, expect suboptimal speed (reason: cannot switch to the 'noop' I/O scheduler: [Errno 22] Invalid argument)
bmaptool: info: 100% copied
bmaptool: info: synchronizing '/dev/sdb'
bmaptool: info: copying time: 7m 36.4s, copying speed 5.2 MiB/sec
Some info from the documentation.
https://www.yoctoproject.org/docs/2.3/dev-manual/dev-manual.html#flashing-images-using-bmaptool
There is an issue with my I/O, but that was already faster for a 7 GB image.