How to stop decryption of external drive I've searched on the internet for a while and asked my question on apples website discussions.apple.com as well, however I haven't found and answer yet and people aren't responding on apple's site so I'd though I'd give it a go here.

So, I have an external drive (1TB) that I made journaled encrypted when I first started using it. By now I also have some video files and pictures on them that I'd wish to show on my TV. However, whilst encrypted I could not view the files other than on a Mac (I was trying to view them on a media player connected to the TV). Thus, I opted for decrypting the drive, since I used up almost 900 GB of the 1TB there are quite a lot of files and I understood the process might take a while.

The thing is, every time I plug the hard drive in it starts taking up storage space. I use a Macbook Pro and don't have a lot of storage space on the macbook itself, hence the external drive and why this is really annoying. To be clear, it is my MacBooks storage space that gets filled up when I plug it in, since this happens every time I can't use the drive on my Macbook anymore either, because every time I can only use it a few minutes before I get warned that "My macbook is almost out of storage space, please remove some files". When I unplug the drive I can literally see the free storage space increasing. So some process is taking up storage space whilst it is working on the drive.

I thought this might be spotlight but I'm not sure since it could also be the decrypting process copying files or something. Is there a way to know why my storage space get filled up, and if its the decrypting, is there a way to stop this process so I can copy my files to another drive? And if it's spotlight is there a way to disable this because putting the drive in the privacy tab of spotlight is somehow also not doable.

I don't mind wiping the drive, but I do mind wiping it without backing up the files on the drive (Yes, in the future I will back up my files better so this won't be an issue again), so a solution to stop the storage filling up is very welcome.

Thanks in advance!
The first thing I would do is open Spotlight system preferences and disable indexing of the external drive. It is a privacy setting.

Next, disconnect from the Internet and restart the Mac with the external drive connected. You might need to free up 5 or 10 GB of space to let things have enough room to sort out the decryption. 

There isn't an abort that I'm aware of, but you can use diskutil cs list to get a reading on the encryption / decryption progress and plan if you want to let it run or if you'll need to take the external drive to another Mac to let it finish. 

If you have a second USB drive, you could install a clean OS onto that drive and hold option. Boot to the empty/vanilla OS on the USB drive and let the external decryption complete.