How BlueStore works

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.

RocksDB

RocksDB is a high-performance key value store, which was originally forked from LevelDB, but after development, Facebook went on to offer significant performance improvements suited for multiprocessor servers with low latency storage devices. It has also had numerous feature enhancements, some of which are used in BlueStore.

RocksDB is used to store metadata about the stored objects, which was previously handled by a combination of LevelDB and XATTRs in filestore.

A feature of RocksDB, which BlueStore takes advantage of, is the ability to store the WAL on...