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57 lines
2.4 KiB
ReStructuredText
57 lines
2.4 KiB
ReStructuredText
===============
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Block Devices
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===============
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A block is a sequence of bytes (for example, a 512-byte block of data).
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Block-based storage interfaces are the most common way to store data with
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rotating media such as hard disks, CDs, floppy disks, and even traditional
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9-track tape. The ubiquity of block device interfaces makes a virtual block
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device an ideal candidate to interact with a mass data storage system like Ceph.
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Ceph block devices are thin-provisioned, resizable and store data striped over
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multiple OSDs in a Ceph cluster. Ceph block devices leverage
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:abbr:`RADOS (Reliable Autonomic Distributed Object Store)` capabilities
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such as snapshotting, replication and consistency. Ceph's
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:abbr:`RADOS (Reliable Autonomic Distributed Object Store)` Block Devices (RBD)
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interact with OSDs using kernel modules or the ``librbd`` library.
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.. ditaa:: +------------------------+ +------------------------+
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| Kernel Module | | librbd |
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+------------------------+-+------------------------+
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| RADOS Protocol |
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+------------------------+-+------------------------+
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| OSDs | | Monitors |
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+------------------------+ +------------------------+
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.. note:: Kernel modules can use Linux page caching. For ``librbd``-based
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applications, Ceph supports `RBD Caching`_.
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Ceph's block devices deliver high performance with infinite scalability to
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`kernel modules`_, or to :abbr:`KVMs (kernel virtual machines)` such as `Qemu`_, and
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cloud-based computing systems like `OpenStack`_ and `CloudStack`_ that rely on
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libvirt and Qemu to integrate with Ceph block devices. You can use the same cluster
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to operate the `Ceph RADOS Gateway`_, the `Ceph FS filesystem`_, and Ceph block
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devices simultaneously.
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.. important:: To use RBD, you must have a running Ceph cluster.
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.. toctree::
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:maxdepth: 1
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Commands <rados-rbd-cmds>
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Kernel Modules <rbd-ko>
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Snapshots<rbd-snapshot>
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QEMU <qemu-rbd>
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libvirt <libvirt>
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Cache Settings <../../config-cluster/rbd-config-ref/>
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OpenStack <rbd-openstack>
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CloudStack <rbd-cloudstack>
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.. _RBD Caching: ../../config-cluster/rbd-config-ref/
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.. _kernel modules: ../rbd-ko/
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.. _Qemu: ../qemu-rbd/
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.. _OpenStack: ../rbd-openstack
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.. _CloudStack: ../rbd-cloudstack
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.. _Ceph RADOS Gateway: ../../radosgw/
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.. _Ceph FS filesystem: ../../cephfs/
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