Although the main driver of BlueStore was not to use an underlying filesystem, BlueStore still needs a method to store RocksDB and the data on the OSD disk. BlueFS was developed, which is an extremely cut down filesystem that provides just the minimal set of features that BlueStore requires. It also means that it has been designed to operate in a dependable manner for the slim set of operations that Ceph submits. It also removes the overhead of the double journal write impact that would be present when using a standard POSIX filesystem.