To this point I have been creating disk images with dd – pretty standard. The command I traditionally use is this:
sudo dd if=/dev/zero of=pc-bsd-10.1.img bs=1M count=40000
This command works but it takes some time as dd copies zeroes for every single part of the image.
It turns out that there is a much faster way to create a disk image, which I found out thanks to this article. Still using dd, you can simply use the -seek parameter to very quickly create your image
sudo dd if=/dev/zero of=pc-bsd-10.1.img bs=1 count=1 seek=40G
By setting bs and count to 1 but seek to 40G I have created a 40 gigabyte empty file image without having to wait for all those pesky zeroes to be written. Awesome.