torouter is intended to boot and run from an SD. it could theoretically also
run from an internal microSD card, a USB stick, or an eSATA drive, but
specifying use of the SD card makes support, development, and documentation
easier. the SD card can easily be popped out of the router and reflashed with a
new image.

The SD card should be at least 2GB in size and support reasonable read/write
speeds, so probably a "class 6" quality card.

you really should get a decent card: there can be an order of magnitude
difference in performance between a cheap card and a fast card. 

quick (but shady?) way to check read and write card performance on a
high-performance machine: 

    $ # unmount the card for read test
    $ hdparm -t /dev/sdb    # iff /dev/sdb is the card
    $ # mount the card for write test
    $ dd count=10 bs=1M if=/dev/urandom of=/mnt/disktest


HOWTO Prepare an SD Card for building (using debian)
--------------------------------------------------------

Insert a 4GB+ SD card into to your dev computer (using an adapter if necessary).

Use lsblk to figure out which block device the card is (eg, /dev/sdc).

Use gparted (as root) to create two logical paritions: first, a 128MB FAT32
(msdos) boot partition, and second an ext4 root partition using the remainder
of the space.

Once the paritions are created, and you have confirmed that the partitions
exist and are in the correct order (eg, small boot on /dev/sdc1, rootfs on
/dev/sdc2), you are ready to copy over a fresh build using
freedom-maker/copy2card.sh and then create an image file using
freedom-maker/copy2img.sh.

Optionally, follow these directions to generate block-aligned partitions for
better write performance:

http://linux-howto-guide.blogspot.de/2009/10/increase-usb-flash-drive-write-speed.html
http://www.olpcnews.com/forum/index.php?topic=4993.0