In computing, Ceph (pronounced or ) is a free-software storage platform, implements object storage on a single distributed computer cluster, and provides interfaces for object-, block- and file-level storage. Ceph aims primarily for completely distributed operation without a single point of failure, scalable to the exabyte level, and freely available.
Ceph replicates data and makes it fault-tolerant, using commodity hardware and requiring no specific hardware support. As a result of its design, the system is both self-healing and self-managing, aiming to minimize administration time and other costs.
On April 21, 2016, the Ceph development team released "Jewel", the first Ceph release in which CephFS is considered stable. The CephFS repair and disaster recovery tools are feature-complete (snapshots, multiple active metadata servers and some other functionality is disabled by default).
The August, 2017 release (codename "Luminous") introduced the production-ready BlueStore storage format which avoids many shortcomings of the old filesystem-based filestore, providing better latency and additional storage features.
Maps, Directions, and Place Reviews
Design
Ceph employs four distinct kinds of daemons:
- Cluster monitors (ceph-mon) that keep track of active and failed cluster nodes
- Metadata servers (ceph-mds) that store the metadata of inodes and directories
- Object storage devices (ceph-osd) that uses a direct, journaled disk storage (named BlueStore, since the v12.x release) or store the content of files in a filesystem (preferably XFS, the storage is named Filestore).
- Representational state transfer (RESTful) gateways (ceph-rgw) that expose the object storage layer as an interface compatible with Amazon S3 or OpenStack Swift APIs
All of these are fully distributed, and may run on the same set of servers. Clients directly interact with all of them.
Ceph does striping of individual files across multiple nodes to achieve higher throughput, similarly to how RAID0 stripes partitions across multiple hard drives. Adaptive load balancing is supported whereby frequently accessed objects are replicated over more nodes. As of September 2017, BlueStore is the default and recommended storage type for production environments, which is Ceph's own storage implementation providing better latency and configurability than the filestore backend, and avoiding the shortcomings of the filesystem based storage involving additional processing and caching layers. The Filestore backend is still considered useful and very stable; XFS is the recommended underlying filesystem type for production environments, while Btrfs is recommended for non-production environments. ext4 filesystems are not recommended because of resulting limitations on the maximum RADOS objects length.
Object storage
Ceph implements distributed object storage. Ceph's software libraries provide client applications with direct access to the reliable autonomic distributed object store (RADOS) object-based storage system, and also provide a foundation for some of Ceph's features, including RADOS Block Device (RBD), RADOS Gateway, and the Ceph File System.
The librados software libraries provide access in C, C++, Java, PHP, and Python. The RADOS Gateway also exposes the object store as a RESTful interface which can present as both native Amazon S3 and OpenStack Swift APIs.
Block storage
Ceph's object storage system allows users to mount Ceph as a thin-provisioned block device. When an application writes data to Ceph using a block device, Ceph automatically stripes and replicates the data across the cluster. Ceph's RADOS Block Device (RBD) also integrates with Kernel-based Virtual Machines (KVMs).
Ceph RBD interfaces with the same Ceph object storage system that provides the librados interface and the CephFS file system, and it stores block device images as objects. Since RBD is built on librados, RBD inherits librados's abilities, including read-only snapshots and revert to snapshot. By striping images across the cluster, Ceph improves read access performance for large block device images.
The block device can be virtualized, providing block storage to virtual machines, in virtualization platforms such as Apache CloudStack, OpenStack, OpenNebula, Ganeti, and Proxmox Virtual Environment.
File system
Ceph's file system (CephFS) runs on top of the same object storage system that provides object storage and block device interfaces. The Ceph metadata server cluster provides a service that maps the directories and file names of the file system to objects stored within RADOS clusters. The metadata server cluster can expand or contract, and it can rebalance the file system dynamically to distribute data evenly among cluster hosts. This ensures high performance and prevents heavy loads on specific hosts within the cluster.
Clients mount the POSIX-compatible file system using a Linux kernel client. On March 19, 2010, Linus Torvalds merged the Ceph client into Linux kernel version 2.6.34 which was released on May 16, 2010. An older FUSE-based client is also available. The servers run as regular Unix daemons.
History
Ceph was initially created by Sage Weil (developer of the Webring concept and co-founder of DreamHost) for his doctoral dissertation, which was advised by Professor Scott A. Brandt in the Jack Baskin School of Engineering at the University of California, Santa Cruz and sponsored by the United States Department of Energy (DOE) and Oak Ridge National Laboratory (ORNL), Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Intel Corporation, Microsoft Corporation, SAP Laboratories and others.
After his graduation in fall 2007, Weil continued to work on Ceph full-time, and the core development team expanded to include Yehuda Sadeh Weinraub and Gregory Farnum. In 2012, Weil created Inktank Storage for professional services and support for Ceph.
In April 2014, Red Hat purchased Inktank, bringing the majority of Ceph development in-house.
In October 2015, the Ceph Community Advisory Board was formed to assist the community in driving the direction of open source software-defined storage technology. The charter advisory board includes Ceph community members from global IT organizations that are committed to the Ceph project, including individuals from Canonical, CERN, Cisco, Fujitsu, Intel, Red Hat, SanDisk, and SUSE.
- Argonaut - on July 3, 2012, the Ceph development team released Argonaut, the first major "stable" release of Ceph. This release will receive stability fixes and performance updates only, and new features will be scheduled for future releases.
- Bobtail (v0.56) - on January 1, 2013, the Ceph development team released Bobtail, the second major stable release of Ceph. This release focused primarily on stability, performance, and upgradability from the previous Argonaut stable series (v0.48.x).
- Cuttlefish (v0.61) - on May 7, 2013, the Ceph development team released Cuttlefish, the third major stable release of Ceph. This release included a number of feature and performance enhancements as well as being the first stable release to feature the 'ceph-deploy' deployment tool in favor of the previous 'mkcephfs' method of deployment.
- Dumpling (v0.67) - on August 14, 2013, the Ceph development team released Dumpling, the fourth major stable release of Ceph. This release included a first pass at global namespace and region support, a REST API for monitoring and management functions, improved support for Red Hat Enterprise Linux derivatives (RHEL)-based platforms.
- Emperor (v0.72) - on November 9, 2013, the Ceph development team released Emperor, the fifth major stable release of Ceph. This release brings several new features, including multi-datacenter replication for the radosgw, improved usability, and lands a lot of incremental performance and internal refactoring work to support upcoming features in Firefly.
- Firefly (v0.80) - on May 7, 2014, the Ceph development team released Firefly, the sixth major stable release of Ceph. This release brings several new features, including erasure coding, cache tiering, primary affinity, key/value OSD backend (experimental), standalone radosgw (experimental).
- Giant (v0.87) - on October 29, 2014, the Ceph development team released Giant, the seventh major stable release of Ceph.
- Hammer (v0.94) - on April 7, 2015, the Ceph development team released Hammer, the eighth major stable release of Ceph. It is expected to form the basis of the next long-term stable series. It is intended to supersede v0.80.x Firefly.
- Infernalis (v9.2.0) - on November 6, 2015, the Ceph development team released Infernalis, the ninth major stable release of Ceph. it will be the foundation for the next stable series. There have been some major changes since v0.94.x Hammer, and the upgrade process is non-trivial.
- Jewel (v10.2.0) - on April 21, 2016, the Ceph development team released Jewel, the first Ceph release in which CephFS is considered stable. The CephFS repair and disaster recovery tools are feature-complete (bidirectional failover, active/active configurations), some functionalities are disabled by default. This release includes new experimental RADOS backend named BlueStore which is planned to be the default storage backend in the upcoming releases.
- Kraken (v11.2.0) - on January 20, 2017, the Ceph development team released Kraken. The new BlueStore storage format, introduced in Jewel, has now a stable on-disk format and is part of the test suite. Despite still marked as experimental, BlueStore is near-production ready, and should be marked as such in the next release, Luminous.
- Luminous (v12.2.0) - on August 29, 2017, the Ceph development team released Luminous. Among other features the BlueStore storage format (using the raw disk instead of a filesystem) is now considered stable and recommended for use.
Etymology
The name "Ceph" is a common nickname given to pet octopuses and derives from cephalopods, a class of molluscs, and ultimately from Ancient Greek ?????? (ke-pha-LEE), meaning "head" and ???? (PO-dhi), meaning "leg". The name (emphasized by the logo) suggests the highly parallel behavior of an octopus and was chosen to connect the file system with UCSC's mascot, a banana slug called "Sammy". Banana slugs are gastropods, which are also a class of molluscs.
Source of the article : Wikipedia
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