...

Additionally, if we supported multiple metadata storage options, we would have to use "least common denominator" APIs.  In other words, we could not use any API unless all possible metadata storage options supported it.  In practice, this would make it difficult to optimize the system.

References

The Raft consensus algorithm

• Ongaro, D., Ousterhout, J. In Search of an Understandable Consensus Algorithm

Handling Metadata via Write-Ahead Logging

• Shvachko, K., Kuang, H., Radia, S. Chansler, R.  The Hadoop Distributed Filesystem
• Balakrishnan, M., Malkhi, D., Wobber, T.  Tango: Distributed Data Structures over a Shared Log