Ceph provides four distinct interfaces to its common storage back end, each designed for a specific type of use case. In this section, we'll describe each and offer a real-world example of how it is used.
The RBD service is perhaps the most familiar, and at many sites is the primary or even only application of Ceph. It presents block (also known as volume) storage in a fashion that with traditional HDD/SDD applications can consume with little or no adjustment. In this way, it is somewhat analogous with facets of VxVM (™), Solaris Disk Suite (SVM)(™), the Linux MD/LVM system, ISCSI or Fibre Channel (™) appliance, or even a ZFS (™) ZVOL. RBD volumes, however, are natively available to multiple servers across the network.
One can build a filesystem directly upon an RBD volume, often as the boot device of a virtual machine in which case the hypervisor is the client of the RBD service and presents the volume to the guest operating system via the virtio or emulation...