In textbooks, the networking stack is TCP (layer-4) --> IP (layer-3) --> Ethernet (layer-2). For storage, the textbook is file format (database or otherwise) --> File system --> Volume --> Drives. The VL2 paper makes the case for a form of "reverse layering" where a layer-2 abstraction is built on top of a specific layer-3 fabric. Many such "reverse layerings" have been proposed in the storage domain as well.
Specifically, a virtual machine's virtual disk is a block abstraction that is materialized as a file (a reverse layering). Describe the implications and argue the pros and cons of that specific form of layering as virtual machines proliferate. Then describe an alternative solution that does not suffer from that same layering, and compare it to the virtual disk abstraction.