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 a faster storage device, which can help to lower latency of RocksDB operations. This also hopefully improves Ceph's performance, particularly for smaller I/Os. This gives a number of possible storage layout configurations, where the WAL, DB, and data can be placed on different storage devices. Three examples are given here:

• WAL, DB, and data all on spinning disk
• WAL and DB on SSD, data on spinning disk
• WAL on NVMe, DB on SSD, and data on spinning disk