To create a CephFS filesystem, two RADOS pools are required: one to store the metadata and another to store the actual data objects. Although technically any existing RADOS pools can be used, it's highly recommended that dedicated pools are created. The metadata pool will typically contain only a small percentage of data when compared to the data pool and, so the number of PGs required when provisioning this pool can typically be set in the 64 - 128 range. The data pool should be provisioned much like an RBD pool and the number of PGs calculated to match the number of OSDs in the cluster and the share of data that the CephFS filesystem will store.
At least one MDS will also need to be deployed, but it is recommended ...
