With nested file systems in some virtualization applications, it is difficult to evaluate the performance of different layers, and to inspect the interaction between them. Even with single layer file systems, sometimes it is desirable to see how the userspace read/writes map to low level file system operations, and further to block layer operations.
Bta analyses traced events happened in different layers of block operations, which are generated by system tracers like lttng. Events are associated with requests from different layers, and the relationship between requests are guessed. Since tracers may not gather all the information for guaranteed correctness, which would degrade the performance of the system.
Currently totally unusable, since I'm still working on first release:).