You need to upload large files (up to 100 GB) to Azure Blob Storage from a web application. The upload must be resilient to network failures and support pausing/resuming. Which approach should you use?
Correct. Block blobs support chunked upload with retry and resume capability.
Why this answer
Option B is correct because block blobs support uploading large files (up to ~4.75 TB) by splitting the file into multiple blocks, uploading them in parallel for speed, and committing the block list atomically. This approach provides resilience to network failures (individual blocks can be retried) and supports pausing/resuming by tracking which blocks have been uploaded.
Exam trap
The trap here is that candidates confuse append blobs with block blobs, thinking append blobs support arbitrary uploads, but append blobs only allow data to be added to the end and cannot be used for random-access or parallel uploads.
How to eliminate wrong answers
Option A is wrong because a single PUT operation is limited to 5 GB (or 256 MB for page blobs), cannot handle 100 GB files, and provides no resilience or pause/resume capability. Option C is wrong because append blobs are designed for append-only operations (e.g., logging), not for uploading large files; they do not support parallel uploads or efficient pause/resume. Option D is wrong because AzCopy is a command-line tool meant for server-side or scripted transfers, not for direct use from a web application; it cannot be integrated into a web app's client-side upload flow.