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115 lines
4.0 KiB
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=============================
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Ceph RADOS Block Device (RBD)
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=============================
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If you use KVM or QEMU as your hypervisor, you can configure the Compute
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service to use `Ceph RADOS block devices
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(RBD) <https://ceph.com/ceph-storage/block-storage/>`__ for volumes.
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Ceph is a massively scalable, open source, distributed storage system.
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It is comprised of an object store, block store, and a POSIX-compliant
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distributed file system. The platform can auto-scale to the exabyte
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level and beyond. It runs on commodity hardware, is self-healing and
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self-managing, and has no single point of failure. Due to its open-source
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nature, you can install and use this portable storage platform in
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public or private clouds.
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.. figure:: ../../figures/ceph-architecture.png
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Ceph architecture
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.. note::
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**Supported Ceph versions**
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The current `release cycle model for Ceph
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<https://docs.ceph.com/en/latest/releases/general/>`_
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targets a new release yearly on 1 March, with there being at most
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two active stable releases at any time.
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For a given OpenStack release, *Cinder supports the current Ceph
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active stable releases plus the two prior releases.*
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For example, at the time of the OpenStack Wallaby release in
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April 2021, the Ceph active supported releases are Pacific and
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Octopus. The Cinder Wallaby release therefore supports Ceph
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Pacific, Octopus, Nautilus, and Mimic.
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Additionally, it is expected that the version of the Ceph client
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available to Cinder or any of its associated libraries (os-brick,
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cinderlib) is aligned with the Ceph server version. Mixing server
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and client versions is *unsupported* and may lead to anomalous behavior.
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RADOS
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~~~~~
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Ceph is based on Reliable Autonomic Distributed Object Store (RADOS).
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RADOS distributes objects across the storage cluster and replicates
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objects for fault tolerance. RADOS contains the following major
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components:
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*Object Storage Device (OSD) Daemon*
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The storage daemon for the RADOS service, which interacts with the
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OSD (physical or logical storage unit for your data).
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You must run this daemon on each server in your cluster. For each
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OSD, you can have an associated hard drive disk. For performance
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purposes, pool your hard drive disk with raid arrays, or logical volume
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management (LVM). By default, the following pools are created: data,
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metadata, and RBD.
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*Meta-Data Server (MDS)*
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Stores metadata. MDSs build a POSIX file
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system on top of objects for Ceph clients. However, if you do not use
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the Ceph file system, you do not need a metadata server.
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*Monitor (MON)*
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A lightweight daemon that handles all communications
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with external applications and clients. It also provides a consensus
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for distributed decision making in a Ceph/RADOS cluster. For
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instance, when you mount a Ceph shared on a client, you point to the
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address of a MON server. It checks the state and the consistency of
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the data. In an ideal setup, you must run at least three ``ceph-mon``
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daemons on separate servers.
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Ways to store, use, and expose data
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To store and access your data, you can use the following storage
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systems:
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*RADOS*
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Use as an object, default storage mechanism.
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*RBD*
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Use as a block device. The Linux kernel RBD (RADOS block
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device) driver allows striping a Linux block device over multiple
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distributed object store data objects. It is compatible with the KVM
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RBD image.
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*CephFS*
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Use as a file, POSIX-compliant file system.
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Ceph exposes RADOS; you can access it through the following interfaces:
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*RADOS Gateway*
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OpenStack Object Storage and Amazon-S3 compatible
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RESTful interface (see `RADOS_Gateway
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<http://docs.ceph.com/docs/master/radosgw/>`__).
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*librados*
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and its related C/C++ bindings
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*RBD and QEMU-RBD*
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Linux kernel and QEMU block devices that stripe
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data across multiple objects.
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Driver options
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~~~~~~~~~~~~~~
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The following table contains the configuration options supported by the
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Ceph RADOS Block Device driver.
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.. config-table::
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:config-target: Ceph storage
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cinder.volume.drivers.rbd
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