https://xrootd.slac.stanford.edu/papers/Scalla-Intro.pdf

The Scalla software suite provides two fundamental building blocks: an xrootd server for low latency high bandwidth data access and an olbd server for building scalable xrootd clusters. This paper describes the architecture, how low latency is achieved, and the scaling opportunities the software allows. Actual performance measurements are presented and discussed. Scalla offers a readily deployable framework in which to construct large fault-tolerant high performance data access configurations using commodity hardware with a minimum amount of administrative overhead.

At first glance EOS is an entire system that adresses all the needs of the researchers at CERN. It includes an object storage with data and metadata separated, which is what the Software Heritage is likely to look like as well. However, this part is not standalone. Although it is a great source of inspiration:

• the choice of Rocksdb and how it is replicated and synchronized with a consensus algorithm for metadata (maybe motivated by the size of the metadata it contains ?)
• the choice of RBD to store data (not the only choice but one of the options)

QuarkDB is now used for namespace. It stores 2.5 billions objects.