Linux Articles listed under "create casper partition"
The following tutorial will show you one way to create a casper-rw partition on your USB flash drive. The benefit of using a casper-rw partition as opposed to a casper-rw block file is that you can expand your persistent storage beyond 4GB. This is very useful if you have a flash drive that is 8GB or larger and you want to use all of it's remaining space for persistent storage. The drawback is that Windows will not see the secondary casper-rw partition (in Windows, your drive will appear to be smaller than it is).