I play to learn. My latest test was educational, and I’m sharing it in case others encounter it.
I ran into problems while playing around with Premium blob storage. I was testing blob storage, comparing performance between Regular and Premium storage, while uploading a 5 MB file. I found my error. I was trying to use block blobs on Premium storage, and only Page Blobs are permitted. But I did not realize that at first. Here was my diagnostic path, with errors to help others who may make the same mistake and search for the errors.