0395353c4b
It was discovered today that the 'config-reference' directory was supposed to have been renamed to 'configuration'. The doc team was expecting it to be at that location so that they could automatically link to it from contributor/index.html . This patch just moves the directory. I am going to be submitting a subsequent patch that properly sets out the framework for the additional directories so that we don't have addition problems in the future. Change-Id: I6729aaf4593a0b089277f6d7d0aa50fee3ca340f
90 lines
4.2 KiB
ReStructuredText
90 lines
4.2 KiB
ReStructuredText
=========================================
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Introduction to the Block Storage service
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=========================================
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The Block Storage service provides persistent block storage
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resources that Compute instances can consume. This includes
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secondary attached storage similar to the Amazon Elastic Block Storage
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(EBS) offering. In addition, you can write images to a Block Storage
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device for Compute to use as a bootable persistent instance.
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The Block Storage service differs slightly from the Amazon EBS offering.
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The Block Storage service does not provide a shared storage solution
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like NFS. With the Block Storage service, you can attach a device to
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only one instance.
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The Block Storage service provides:
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- ``cinder-api`` - a WSGI app that authenticates and routes requests
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throughout the Block Storage service. It supports the OpenStack APIs
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only, although there is a translation that can be done through
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Compute's EC2 interface, which calls in to the Block Storage client.
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- ``cinder-scheduler`` - schedules and routes requests to the appropriate
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volume service. Depending upon your configuration, this may be simple
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round-robin scheduling to the running volume services, or it can be
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more sophisticated through the use of the Filter Scheduler. The
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Filter Scheduler is the default and enables filters on things like
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Capacity, Availability Zone, Volume Types, and Capabilities as well
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as custom filters.
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- ``cinder-volume`` - manages Block Storage devices, specifically the
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back-end devices themselves.
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- ``cinder-backup`` - provides a means to back up a Block Storage volume to
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OpenStack Object Storage (swift).
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The Block Storage service contains the following components:
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- **Back-end Storage Devices** - the Block Storage service requires some
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form of back-end storage that the service is built on. The default
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implementation is to use LVM on a local volume group named
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"cinder-volumes." In addition to the base driver implementation, the
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Block Storage service also provides the means to add support for
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other storage devices to be utilized such as external Raid Arrays or
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other storage appliances. These back-end storage devices may have
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custom block sizes when using KVM or QEMU as the hypervisor.
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- **Users and Tenants (Projects)** - the Block Storage service can be
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used by many different cloud computing consumers or customers
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(tenants on a shared system), using role-based access assignments.
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Roles control the actions that a user is allowed to perform. In the
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default configuration, most actions do not require a particular role,
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but this can be configured by the system administrator in the
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appropriate ``policy.json`` file that maintains the rules. A user's
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access to particular volumes is limited by tenant, but the user name
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and password are assigned per user. Key pairs granting access to a
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volume are enabled per user, but quotas to control resource
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consumption across available hardware resources are per tenant.
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For tenants, quota controls are available to limit:
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- The number of volumes that can be created.
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- The number of snapshots that can be created.
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- The total number of GBs allowed per tenant (shared between
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snapshots and volumes).
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You can revise the default quota values with the Block Storage CLI,
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so the limits placed by quotas are editable by admin users.
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- **Volumes, Snapshots, and Backups** - the basic resources offered by
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the Block Storage service are volumes and snapshots which are derived
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from volumes and volume backups:
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- **Volumes** - allocated block storage resources that can be
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attached to instances as secondary storage or they can be used as
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the root store to boot instances. Volumes are persistent R/W block
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storage devices most commonly attached to the compute node through
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iSCSI.
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- **Snapshots** - a read-only point in time copy of a volume. The
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snapshot can be created from a volume that is currently in use
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(through the use of ``--force True``) or in an available state.
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The snapshot can then be used to create a new volume through
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create from snapshot.
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- **Backups** - an archived copy of a volume currently stored in
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Object Storage (swift).
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