60 lines
2.3 KiB
ReStructuredText
60 lines
2.3 KiB
ReStructuredText
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.. _storage-ha-backend:
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================
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Storage back end
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================
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An OpenStack environment includes multiple data pools for the VMs:
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- Ephemeral storage is allocated for an instance and is deleted when the
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instance is deleted. The Compute service manages ephemeral storage and
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by default, Compute stores ephemeral drives as files on local disks on the
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compute node. As an alternative, you can use Ceph RBD as the storage back
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end for ephemeral storage.
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- Persistent storage exists outside all instances. Two types of persistent
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storage are provided:
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- The Block Storage service (cinder) that can use LVM or Ceph RBD as the
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storage back end.
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- The Image service (glance) that can use the Object Storage service (swift)
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or Ceph RBD as the storage back end.
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For more information about configuring storage back ends for
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the different storage options, see `Manage volumes
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<https://docs.openstack.org/admin-guide/blockstorage-manage-volumes.html>`_
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in the OpenStack Administrator Guide.
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This section discusses ways to protect against data loss in your OpenStack
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environment.
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RAID drives
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-----------
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Configuring RAID on the hard drives that implement storage protects your data
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against a hard drive failure. If the node itself fails, data may be lost.
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In particular, all volumes stored on an LVM node can be lost.
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Ceph
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----
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`Ceph RBD <https://ceph.com/>`_ is an innately high availability storage back
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end. It creates a storage cluster with multiple nodes that communicate with
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each other to replicate and redistribute data dynamically.
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A Ceph RBD storage cluster provides a single shared set of storage nodes that
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can handle all classes of persistent and ephemeral data (glance, cinder, and
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nova) that are required for OpenStack instances.
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Ceph RBD provides object replication capabilities by storing Block Storage
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volumes as Ceph RBD objects. Ceph RBD ensures that each replica of an object
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is stored on a different node. This means that your volumes are protected
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against hard drive and node failures, or even the failure of the data center
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itself.
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When Ceph RBD is used for ephemeral volumes as well as block and image storage,
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it supports `live migration
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<https://docs.openstack.org/admin-guide/compute-live-migration-usage.html>`_
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of VMs with ephemeral drives. LVM only supports live migration of
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volume-backed VMs.
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