86 lines
2.7 KiB
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86 lines
2.7 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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Most of this guide concerns the control plane of high availability:
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ensuring that services continue to run even if a component fails.
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Ensuring that data is not lost
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is the data plane component of high availability;
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this is discussed here.
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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
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and is deleted when the instance is deleted.
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The Compute service manages ephemeral storage.
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By default, Compute stores ephemeral drives as files
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on local disks on the Compute node
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but Ceph RBD can instead be used
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as the storage back end for ephemeral storage.
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- Persistent storage exists outside all instances.
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Two types of persistent storage are provided:
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- Block Storage service (cinder)
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can use LVM or Ceph RBD as the storage back end.
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- Image service (glance)
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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 the `Administrator Guide
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<http://docs.openstack.org/admin-guide/>`_.
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This section discusses ways to protect against
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data loss in your OpenStack environment.
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RAID drives
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-----------
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Configuring RAID on the hard drives that implement storage
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protects your data against a hard drive failure.
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If, however, 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 <http://ceph.com/>`_
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is an innately high availability storage back end.
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It creates a storage cluster with multiple nodes
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that communicate with each other
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to replicate and redistribute data dynamically.
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A Ceph RBD storage cluster provides
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a single shared set of storage nodes
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that can handle all classes of persistent and ephemeral data
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-- glance, cinder, and nova --
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that are required for OpenStack instances.
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Ceph RBD provides object replication capabilities
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by storing Block Storage volumes as Ceph RBD objects;
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Ceph RBD ensures that each replica of an object
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is stored on a different node.
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This means that your volumes are protected against
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hard drive and node failures
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or even the failure of the data center itself.
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When Ceph RBD is used for ephemeral volumes
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as well as block and image storage, it supports
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`live migration
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<http://docs.openstack.org/admin-guide/compute-live-migration-usage.html>`_
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of VMs with ephemeral drives;
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LVM only supports live migration of volume-backed VMs.
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Remote backup facilities
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------------------------
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[TODO: Add discussion of remote backup facilities
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as an alternate way to secure ones data.
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Include brief mention of key third-party technologies
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with links to their documentation]
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