How to save a large array on disk

I would like to save a large array(too large to store in memory), each element to the designated positon. Also, I want to modify it in procedure.

Can TTree make it?

I mean, fill the TTree with nEntry 0. in advance, and then modify some element on the designated position, is it possible?

Or if there is any faster way.

Thanks a lot

See tutorials tree2.C or tree3.C