[acdha]

I've seen this an an outgrowth of the file storage world:

1. Flat data model – i.e. no directories, just a single globally-unique identifier 2. Much larger sizes than many key:value stores are designed to handle, typically bounded only by physical storage 3. Updates are complete and atomic: you don't have to support all of the crazy permutations like streaming writes from a file handle which could be kept open for years, dealing with simultaneous writes, etc. which make life interesting for filesystem implementers 4. None of the more complicated filesystem behaviour like locking, alternate data streams, etc. which add so many edge cases