Here's a neat little trick which should be useful for anyone needing to flash the same SD card .img onto lots of SD cards in parallel. We have been using it to load up the Raspberry Pi pre-loaded emoncms gateway SD cards. Thanks to @dpslwk for the initial idea.
Tested on Ubuntu Linux 13.10 64-bit
First install dcfldd which is an enhanced version of dd
$ sudo apt-get install dcfldd
I used a USB hub with five SD card readers
$ sudo fdisk -l
can be used to determine the drive letter of the SD cards, depending on your hard disk configuration it will usually be something like /dev/sdx where x is b-f. Make sure you check this carefully, selecting the wrong disk can result in one of your hard drives being wiped! dd is not nicknamed 'delete disk' for nothing!
Finally run dcfld selecting each SD card as the output file:
$ sudo dcfldd if=SD_CARD_IMAGE.img bs=4M sizeprobe=if of=/dev/sdb of=/dev/sdc of=/dev/sdd of=/dev/sde of=/dev/sdf
Flashing five SD cards with a 2GB image takes about 4 min for me:
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