Introduction

RADOS

Reliable Autonomic Distributed Object Store (RADOS) is the heart of a Ceph storage cluster. Everything in Ceph is stored by RADOS in the form of objects irrespective of their data types. The RADOS layer ensures data consistency and reliability through data replication, fault detection and recovery, and data recovery across cluster nodes.

OSD

Object storage daemons (OSDs) store the actual user data. Every OSD is usually bound to one physical drive. The OSDs handle the read/write requests from clients.

MON

The monitor (MON) is the most important component in a Ceph cluster. It manages the Ceph cluster and maintains the status of the entire cluster. The MON ensures that related components of a cluster can be synchronized at the same time. It functions as the leader of the cluster and is responsible for collecting, updating, and publishing cluster information. To avoid single points of failure (SPOFs), multiple MONs are deployed in a Ceph environment, and they must handle the collaboration between them.

MGR

The manager (MGR) is a monitoring system that provides collection, storage, analysis (including alarming), and visualization functions. It makes certain cluster parameters available for external systems.

LIBRADOS

Librados is a method that simplifies access to RADOS. Currently, it supports programming languages PHP, Ruby, Java, Python, C, and C++. It provides RADOS, a local interface of the Ceph storage cluster, and is the base component of other services such as the RADOS block device (RBD) and RADOS gateway (RGW). In addition, it provides the Portable Operating System Interface (POSIX) for the Ceph file system (CephFS). The Librados API can be used to directly access RADOS, enabling developers to create their own interfaces for accessing the Ceph cluster storage.

RBD

The RADOS block device (RBD) is the Ceph block device that provides block storage for external systems. It can be mapped, formatted, and mounted like a drive to a server.

RGW

The RADOS gateway (RGW) is a Ceph object gateway that provides RESTful APIs compatible with S3 and Swift. The RGW also supports multi-tenant and OpenStack Identity service (Keystone).

MDS

The Ceph Metadata Server (MDS) tracks the file hierarchy and stores metadata used only for CephFS. The RBD and RGW do not require metadata. The MDS does not directly provide data services for clients.

CephFS

The CephFS provides a POSlX-compatible distributed file system of any size. It depends on the Ceph MDS to track the file hierarchy, namely the metadata.