Seems it has a modular storage back-end[0], the default uses a built-in storage engine local files with oCIS storage driver [1].

[0] https://owncloud.github.io/ocis/storage-backends/eos/

[1] "The default oCIS storage driver deconstructs a filesystem to be able to efficiently look up files by fileid as well as path. It stores all folders and files by a uuid and persists share and other metadata using extended attributes. This allows using the linux VFS cache using stat syscalls instead of a database or key/value store. The driver implements trash, versions and sharing. It not only serves as the current default storage driver, but also as a blueprint for future storage driver implementations."

With this design we aim for the storage to become the single-point of truth and scale-out as the metadata is spatially close to the files.