No reason for the receiver to become unusable by simply adding a drive that I know about.
If you carefully read the links I provided, I think most menus and options for storage will be explained. I do not mind explaining in detail, but there is no reason if the information needed already exists.
Most of these settings are what you want them to be or what they need to be. Let me explain:
The correct path for PVR storage will be the correct path for the device you want to be your PVR storage. If you want to use the usb stick, then point your PVR storage to its correct path.
If you have a decent LAN, by decent meaning enough speed to record and do whatever else you want to do at the same time, then you may want to point the PVR storage path to one of your network shares and have the PVR recordings dump straight into a computer or a router's storage for example.
Pretty much any healthy usb drive that does not require external power can be plugged directly into the receiver and used "As Is" If you are having problems with a good usb drive that works on your home computer or laptop for example, but is not "Seen" by the receiver, then we need to look at it and found out why. A reboot may be needed after the USB drive is installed before it becomes usable.
And we have a dandy little way of looking into the receiver files using the receiver itself. The Dream-Explorer plugin allows you to look at the files system, so you can verify the usb drive is installed and seen by the receiver using the Dream-Explorer plugin. Any external drives will most likely be in /media of receiver files once they are recognized after a REBOOT.
Basically, the enigma2 receiver is a stripped version of Linux and will operate the same or usually similar to other Linux computers when it comes to storage devices. Linux can "see" most formats of a drive, but Windows for example cannot "see" some Linux drives. This is why i say most any usb drive you stick into the receiver should be recognized and usable for PVR storage, provided the receiver is properly pointed to it.