144 lines
7.1 KiB
XML
144 lines
7.1 KiB
XML
<section xml:id="ceph-rados" xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0">
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<title>Ceph RADOS Block Device (RBD)</title>
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<para>By Sebastien Han from <link
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xlink:href="http://www.sebastien-han.fr/blog/2012/06/10/introducing-ceph-to-openstack/"
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/></para>
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<para>If you use KVM or QEMU as your hypervisor, you can configure
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the Compute service to use <link
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xlink:href="http://ceph.com/ceph-storage/block-storage/">
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Ceph RADOS block devices (RBD)</link> for volumes.</para>
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<para>Ceph is a massively scalable, open source, distributed
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storage system. It is comprised of an object store, block
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store, and a POSIX-compliant distributed file system. The
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platform can auto-scale to the exabyte level and beyond. It
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runs on commodity hardware, is self-healing and self-managing,
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and has no single point of failure. Ceph is in the Linux
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kernel and is integrated with the OpenStack cloud operating
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system. Due to its open source nature, you can install and use
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this portable storage platform in public or private clouds. <figure>
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<title>Ceph architecture</title>
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<mediaobject>
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<imageobject>
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<imagedata
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fileref="../../../common/figures/ceph/ceph-architecture.png"
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contentwidth="6in"/>
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</imageobject>
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</mediaobject>
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</figure>
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</para>
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<simplesect>
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<title>RADOS?</title>
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<para>You can easily get confused by the naming: Ceph?
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RADOS?</para>
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<para><emphasis>RADOS: Reliable Autonomic Distributed Object
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Store</emphasis> is an object store. RADOS distributes
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objects across the storage cluster and replicates objects
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for fault tolerance. RADOS contains the following major
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components:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>Object Storage Device
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(ODS)</emphasis>. The storage daemon - RADOS
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service, the location of your data. You must run
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this daemon on each server in your cluster. For
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each OSD, you can have an associated hard drive
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disks. For performance purposes, pool your hard
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drive disk with raid arrays, logical volume
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management (LVM) or B-tree file system (Btrfs)
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pooling. By default, the following pools are
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created: data, metadata, and RBD.</para>
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</listitem>
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<listitem>
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<para><emphasis>Meta-Data Server (MDS)</emphasis>.
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Stores metadata. MDSs build a POSIX file system on
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top of objects for Ceph clients. However, if you
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do not use the Ceph file system, you do not need a
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metadata server.</para>
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</listitem>
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<listitem>
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<para><emphasis>Monitor (MON)</emphasis>. This
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lightweight daemon handles all communications with
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external applications and clients. It also
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provides a consensus for distributed decision
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making in a Ceph/RADOS cluster. For instance, when
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you mount a Ceph shared on a client, you point to
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the address of a MON server. It checks the state
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and the consistency of the data. In an ideal
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setup, you must run at least three
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<code>ceph-mon</code> daemons on separate
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servers.</para>
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</listitem>
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</itemizedlist>
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<para>Ceph developers recommend that you use Btrfs as a file
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system for storage. XFS might be a better alternative for
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production environments. Neither Ceph nor Btrfs is ready
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for production and it could be risky to use them in
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combination. XFS is an excellent alternative to Btrfs. The
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ext4 file system is also compatible but does not exploit
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the power of Ceph.</para>
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<note>
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<para>Currently, configure Ceph to use the XFS file
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system. Use Btrfs when it is stable enough for
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production.</para>
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</note>
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<para>See <link
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xlink:href="http://ceph.com/docs/master/rec/filesystem/"
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>ceph.com/docs/master/rec/file system/</link> for more
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information about usable file systems.</para>
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</simplesect>
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<simplesect>
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<title>Ways to store, use, and expose data</title>
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<para>To store and access your data, you can use the following
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storage systems:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>RADOS</emphasis>. Use as an object,
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default storage mechanism.</para>
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</listitem>
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<listitem>
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<para><emphasis>RBD</emphasis>. Use as a block device.
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The Linux kernel RBD (rados block device) driver
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allows striping a Linux block device over multiple
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distributed object store data objects. It is
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compatible with the kvm RBD image.</para>
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</listitem>
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<listitem>
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<para><emphasis>CephFS</emphasis>. Use as a file,
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POSIX-compliant file system.</para>
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</listitem>
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</itemizedlist>
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<para>Ceph exposes its distributed object store (RADOS). You
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can access it through the following interfaces:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>RADOS Gateway</emphasis>. Swift and
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Amazon-S3 compatible RESTful interface. See <link
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xlink:href="http://ceph.com/wiki/RADOS_Gateway"
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>RADOS_Gateway</link> for more
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information.</para>
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</listitem>
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<listitem>
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<para><emphasis>librados</emphasis>, and the related
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C/C++ bindings.</para>
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</listitem>
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<listitem>
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<para><emphasis>rbd and QEMU-RBD</emphasis>. Linux
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kernel and QEMU block devices that stripe data
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across multiple objects.</para>
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</listitem>
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</itemizedlist>
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<para>For detailed installation instructions and benchmarking
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information, see <link
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xlink:href="http://www.sebastien-han.fr/blog/2012/06/10/introducing-ceph-to-openstack/"
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>http://www.sebastien-han.fr/blog/2012/06/10/introducing-ceph-to-openstack/</link>.</para>
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</simplesect>
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<simplesect>
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<title>Driver Options</title>
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<para>The following table contains the configuration options
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supported by the Ceph RADOS Block Device driver.</para>
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<xi:include href="../../../common/tables/cinder-storage_ceph.xml" />
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</simplesect>
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</section>
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