Add new disk drive to Linux file system

I have some new hard drive space and I need to add it to both the / file system and /usr/local system. I don't know if this is possible. If not, then I need to add it to the / file system. I would like complete instructions and commands on how I can do this. I changed FSTAB and did a mount and was able to replace the current /usr/local system. But I would like to ADD the space to what already exists. There is a lot on both the / and /usr/local file systems. ## Deliverables 1) Complete and fully-functional added disk drive to file system. ## Platform Linux