How to utilise all useful space of a raid 1 btrfs cache pool?

[walle]

I recently added a 1 tb SSD to my existing 2x 500 gb SSD cache pool. As I understand it, I should have 1 tb useful space for file storage(source: the btrfs disk usage calculator). However GUI indicates I only have round 570 GB (432+139) useful storage.

 

Have I missed something? What's the reason I don't get 1 tb with raid 1?

 

Edited March 5 by walle

[JorgeB]

1 minute ago, walle said:

However GUI indicates I only have round 570 GB (432+139) useful storage.

That's normal with an odd number of devices and btrfs, used space will be correct and free space will get closer to correct as you fill up the pool.