Block storage?

Is there a way to save blocks inside code without having to create a backup and then reset those blocks again?

Upon block related events, save original blocks into an array and place the original blocks when you want to restore it.

I already do that but, won't that be too large for a single array?

I guess you can sort the blocks out depending on block ID, Y coordinate or player who triggered it, or you can make a new array when the other arrays have 100 data stored, but either way, you would end up with a large amount of data.
Does something bad happen if there are too many objects in one array, though?

Array is unlimited, but it takes up memory so that's why it would be a problem.

That's why Minecraft world is in chunks. Write it on file and compress it.