Windows shares copy/move problems laso truenas missing features?

I’ve lots of files and folders to transfer from one pool to another and these folders have windows shares. I am doing this to rebalance the pool after adding 2 more disks. I’ve previously tried rebalancing script given in these forums but it gave me permission errors so i decided to it manually. However same problems occured when doing this manually. When i try to move files while keeping permissions it started to give me errors so i stopped it although it moved some files. My question is what kind of headache can it cause to me if i move files like this? I tried accessing some moved files and i can still run them.

Also my other question is as far as i know when you add 2 more disks as a mirror to a pool which does also have a mirror, you double performance right? but there is no tool inside truenas(as far as i know) to rebalance the pool to be able to actually reach the speed like this? So what am i missing here? Does everybody move files from one place to another when add new disks to their pools to be able to have the performance benefits? I am a regular home user and even i had to transfer 5 tb of files for this. I cant think of people with big servers.

Thanks in advance.

You can replicate datasets.

It’s not quite the same as moving files as the old dataset will still exist.

Personally I’ve never bothered.