Azure blob's block list is empty, but blob is not empty! How can this be?

Question

This issue in a nutshell:

A block blob can be created with a single PUT request. This will create a blob with committed content but the blob will

Answer 1

As you also identified with your tests, querying the list of blocks of a block blob uploaded using Put Blob will return an empty list. This is by design.

UploadFromStream API in the Storage Client Library makes a couple of checks before deciding whether to upload a blob using a single Put Blob operation or a sequence of Put Block operations followed by a Put Block List. One property that changes this behavior is SingleBlobUploadThresholdInBytes.