The following diagram shows how BlueStore interacts with a block device. Unlike filestore, data is directly written to the block device and metadata operations are handled by RocksDB:

The block device is divided between RocksDB data storage and the actual user data stored in Ceph. Each object is stored as a number of blobs allocated from the block device. RocksDB contains metadata for each object and tracks the utilization and allocation information for the data blobs.