I'm running Ubuntu off an 8gb USB drive but it's almost full; is there a way to install my applications on a different USB drive. It's been suggested that RAID 1 will work but will that just duplicate my files?
Unlike Windows, there is no easy way to choose the installation directory in Ubuntu.
A full install may be easier to manage. For example, you could uninstall the older kernels. the persistent USB works off the CD image and stuff that came in the ISO can't be easily removed even when they are updated.
I suggest backup all the data saved in the USB somewhere else (may be another USB drive) and try full install: How do I install Ubuntu to a USB key?.
RAID 1 mirrors one drive to another in real time. So if one fails the other can take over its duties. So adding another drive in RAID 1 formation does not add any disk space.
RAID 0 strips, that is divides up all the data between two drives. This makes reading and writing faster, but if one fails everything is history, as you will have half of each file.
RAID was intended for identical internal drives that don't get moved around. USB drives and flash drives are external and intended to be plugged and unplugged and moved between computers. However, plugging and unplugging them may give them different internal IDs. If that happens one part of RAID0 won't recognize the other part and the system will fail as you will have half of everything, including the OS.