I don't exist on my own.
With me the thing I belong to is seen as a whole.
What I belong to and am a part of is usually only created once and I along with it.
In all cases my size can only be adjusted during the creation of the thing I'm a part of.
In close to all cases my count can only be set during the creation of the thing I'm a part of.
If the thing I'm a part of is causing you grief when nothing seems to be wrong, it's time to look into me.
ls, find, and a few other commands have options for you to view/find information about me and what I contain.
I possess vital data for the thing I belong to and without it they are useless.

It's hard to come up with clues that don't reveal too much but give you enough to get it. When you know the answer the clues seem so obvious. I apologize for before, hopefully this is better.