[hboon]

In addition,

It doesn't have good querying utilities. You'd have to build your own indexer and query engine. Since you can't put billions of files in a single directory, you'd have to split them into a directory tree. That alone requires some basic indexing functionality and rebalancing tools (in case a single directory grows too large or too small). This is without any more sophisticated querying capabilities like “where X=val” where X isn't the object ID/filename.

Write performance is going to be very very horrible.

Existing tools around managing, backing up and restoration, performance optimisation and monitoring aren't suitable for handling huge number of small files as well as a subset of them (give certain criteria related to the data itself)

You could build specialized tools to resolve all of these issues, but in the end, you'd end up with some kind of database after hundreds of man-years anyway.