7ac18a94b8
backport: havana Change-Id: I0936caed5cac45373df9bbc077f66bcfa2f96b58 Partial-Bug: #1121866
133 lines
7.0 KiB
XML
133 lines
7.0 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section 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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xml:id="section_block-storage-overview">
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<title>Introduction to the Block Storage Service</title>
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<para>The Openstack Block Storage Service provides persistent
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block storage resources that OpenStack Compute instances can
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consume. This includes secondary attached storage similar to
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the Amazon Elastic Block Storage (EBS) offering. In addition,
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you can write images to a Block Storage device for
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Compute to use as a bootable persistent
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instance.</para>
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<para>The Block Storage Service differs slightly from
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the Amazon EBS offering. The Block Storage Service
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does not provide a shared storage solution like NFS. With the
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Block Storage Service, you can attach a device to
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only one instance.</para>
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<para>The Block Storage Service provides:</para>
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<itemizedlist>
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<listitem>
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<para><systemitem class="service">cinder-api</systemitem>. A WSGI
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app that authenticates and routes requests throughout
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the Block Storage Service. It supports the OpenStack
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APIs only, although there is a translation that can be
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done through Compute's EC2 interface, which calls in to
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the cinderclient.</para>
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</listitem>
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<listitem>
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<para><systemitem class="service">cinder-scheduler</systemitem>. Schedules and routes requests
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to the appropriate volume service. As of Grizzly; depending upon your configuration
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this may be simple round-robin scheduling to the running volume services, or it can
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be more sophisticated through the use of the Filter Scheduler. The Filter Scheduler
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is the default in Grizzly and enables filters on things like Capacity, Availability
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Zone, Volume Types, and Capabilities as well as custom filters.</para>
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</listitem>
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<listitem>
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<para><systemitem class="service">cinder-volume</systemitem>.
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Manages Block Storage devices, specifically the
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back-end devices themselves.</para>
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</listitem>
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<listitem>
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<para><systemitem class="service">cinder-backup</systemitem>
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Provides a means to back up a Block Storage Volume
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to OpenStack Object Store (SWIFT).</para>
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</listitem>
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</itemizedlist>
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<para>The Block Storage Service contains the following
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components:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis role="bold">Back-end Storage
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Devices</emphasis>. The Block Storage
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Service requires some form of back-end storage that
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the service is built on. The default implementation is
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to use LVM on a local volume group named
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"cinder-volumes." In addition to the base driver
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implementation, the Block Storage Service
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also provides the means to add support for other
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storage devices to be utilized such as external Raid
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Arrays or other storage appliances. These back-end storage devices
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may have custom block sizes when using KVM or QEMU as the hypervisor.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Users and Tenants
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(Projects)</emphasis>. The Block Storage
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Service is designed to be used by many different cloud
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computing consumers or customers, basically tenants on
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a shared system, using role-based access assignments.
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Roles control the actions that a user is allowed to
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perform. In the default configuration, most actions do
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not require a particular role, but this is
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configurable by the system administrator editing the
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appropriate <filename>policy.json</filename> file that
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maintains the rules. A user's access to particular
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volumes is limited by tenant, but the username and
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password are assigned per user. Key pairs granting
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access to a volume are enabled per user, but quotas to
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control resource consumption across available hardware
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resources are per tenant.</para>
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<para>For tenants, quota controls are available to
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limit:</para>
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<itemizedlist>
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<listitem>
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<para>The number of volumes that can be
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created</para>
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</listitem>
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<listitem>
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<para>The number of snapshots that can be
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created</para>
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</listitem>
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<listitem>
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<para>The total number of GBs allowed per tenant
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(shared between snapshots and volumes)</para>
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</listitem>
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</itemizedlist>
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<para>You can revise the default quota values with the cinder CLI, so the limits placed by quotas are editable by admin users.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Volumes, Snapshots, and
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Backups</emphasis>. The basic resources offered by
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the Block Storage Service are volumes and
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snapshots, which are derived from volumes, and
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backups:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis role="bold">Volumes</emphasis>.
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Allocated block storage resources that can be
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attached to instances as secondary storage or
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they can be used as the root store to boot
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instances. Volumes are persistent R/W block
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storage devices most commonly attached to the
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Compute node through iSCSI.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Snapshots</emphasis>.
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A read-only point in time copy of a volume.
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The snapshot can be created from a volume that
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is currently in use (through the use of
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'--force True') or in an available state. The
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snapshot can then be used to create a new
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volume through create from snapshot.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Backups</emphasis>. An
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archived copy of a volume currently stored in
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OpenStack Object Storage (Swift).</para>
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</listitem>
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</itemizedlist>
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</listitem>
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</itemizedlist>
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</section>
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