Do I have to have fencing configured to quorum disk work properly?
- If this is 'just' an exercise and meant to get some understanding in (Red Hat) clustering: No you don't need it, as long as you know/understand what manual fencing does (and doesn't!) and its place in the bigger picture. At certain points your cluster will not react as described in the docs/manuals (that is a given! and very annoying at times) because manual fencing isn't set up and/or isn't configured properly.
- If this cluster is for real: Yes you do. A quorum disk is needed to end up with an uneven amount of nodes, without an uneven amount of nodes fencing cannot properly decide which is the 'bad node'. You could decide, if you have the resources, to add a third physical node and drop the quorum disk. But that leaves you with manual fencing. As I stated before, manual fencing should not be used other then testing, evaluation or be used as a last resort fallback next to 'real' fencing.