I was trying to install Ubuntu live on a USB-drive with persistent changes. However i wanted to write the changes to HDD instead of USB for various reasons (Performance, Space).
I found out, that the changes are handled within a file with a ext3 file-system that is mounted by the system (casper-rw). But it seem to be auto-detected on flash-drive on startup.
How can i create a new casper-rw file on HDD and reroute the Ubuntu live system on the USB-drive to HDD?
Thank you for the answers so far. They are very interesting and help a lot to understand the mechanics of the "live system persistent save feature" better, and show good approaches to solve the problem. Unfortunately i was trying to overcome some limitations that i had in mind when asking the question regarding access to the host system and/or access to new hardware i did not clearly state (sorry for that).
If partitioning is an option, i think the answer stated here is very good, since it only requires you to create a new partition, label it casper-rw and you're done (work's great, i tested it).
If buying new hardware is an option, usb3.0 Flash-Drive (MLC or SLC), portable HDDs, eSATA and other options come to mind that have a far better performance than an average USB2.0 flash-drive.
So i was wondering if there is a way to just create a casper-rw file instead of a partition on a disk with limited access to (or copy/link the one on the flash-drive).
This way it would be easy to just copy the casper-rw file back to the flash-drive and use it from there again or move it to an other computer, granting great flexibility, minimal changes to the HDD and easy removal of changes done to the system.