expanding thick provisioned disk?

I had a 30TB drive that was originally thin provisioned - VMFS 5. Then I learned that if you delete files in the OS, the reduction in size isn't reflected in the datastore. Reclaiming the space by shutting down the vm, then mounting the drive elsewhere and zeroing out the free space wasn't really an option. So I converted it to thick provisioned eager zeroed. This took over 24 hours to complete - so I hope to never have to do that again. Now I'm needing to extend the disk - however I have read conflicting info and wondering what the best way to do this will be with minimal downtime. I read that if I shut down the VM, then extend the drive - this will actually convert it to thin provisioned so that the space can be extended. Is this correct?! Would this result in another 24+ hours of downtime? I also read that using commandline tools, you can tell it to leave the new space thick provisioned without doing the conversion. Is this correct? If so, it seems like that might be better...assuming its not going to take 24 hours to complete. What is the best course of action here? (if I could do this over, I would not have 1 huge disk, instead several smaller ones...but here I am)