A year ago, I created an e2-medium with 10GB standard persistent disk in us-central1. As expected, It did not cost me for Storage due to Free Tier for Compute Engine. Months ago, I created an e2-medium with 20GB standard persistent disk in asia-southeast1-b. And it charges me for Storage Disk regardless of Free Tier.
Why is it? I thought I still use totally 30GB of Free Tier Compute Engine. Or I have to create instance in supported regions such as us-central1, us-west1, asia-east1 ?