<commit_before><?xml version="1.0" encoding="utf-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
  xmlns:xi="http://www.w3.org/2001/XInclude"
  xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
  xml:id="module001-ch011-block-storage">
  <title>OpenStack Block Storage</title>
  <para><emphasis role="bold">Block Storage and OpenStack
      Compute</emphasis></para>
  <para>OpenStack provides two classes of block storage, "ephemeral"
    storage and persistent "volumes". Ephemeral storage exists only
    for the life of an instance, it will persist across reboots of the
    guest operating system but when the instance is deleted so is the
    associated storage. All instances have some ephemeral storage.
    Volumes are persistent virtualized block devices independent of
    any particular instance. Volumes may be attached to a single
    instance at a time, but may be detached or reattached to a
    different instance while retaining all data, much like a USB
    drive.</para>
  <para><guilabel>Ephemeral Storage</guilabel></para>
  <para>Ephemeral storage is associated with a single unique instance.
    Its size is defined by the flavor of the instance.</para>
  <para>Data on ephemeral storage ceases to exist when the instance it
    is associated with is terminated. Rebooting the VM or restarting
    the host server, however, will not destroy ephemeral data. In the
    typical use case an instance's root filesystem is stored on
    ephemeral storage. This is often an unpleasant surprise for people
    unfamiliar with the cloud model of computing.</para>
  <para>In addition to the ephemeral root volume all flavors except
    the smallest, m1.tiny, provide an additional ephemeral block
    device varying from 20G for the m1.small through 160G for the
    m1.xlarge by default - these sizes are configurable. This is
    presented as a raw block device with no partition table or
    filesystem. Cloud aware operating system images may discover,
    format, and mount this device. For example the cloud-init package
    included in Ubuntu's stock cloud images will format this space as
    an ext3 filesystem and mount it on /mnt. It is important to note
    this a feature of the guest operating system. OpenStack only
    provisions the raw storage.</para>
  <para><guilabel>Volume Storage</guilabel></para>
  <para>Volume storage is independent of any particular instance and
    is persistent. Volumes are user created and within quota and
    availability limits may be of any arbitrary size.</para>
  <para>When first created volumes are raw block devices with no
    partition table and no filesystem. They must be attached to an
    instance to be partitioned and/or formatted. Once this is done
    they may be used much like an external disk drive. Volumes may
    attached to only one instance at a time, but may be detached and
    reattached to either the same or different instances.</para>
  <para>It is possible to configure a volume so that it is bootable
    and provides a persistent virtual instance similar to traditional
    non-cloud based virtualization systems. In this use case the
    resulting instance may still have ephemeral storage depending on
    the flavor selected, but the root filesystem (and possibly others)
    will be on the persistent volume and thus state will be maintained
    even if the instance it shutdown. Details of this configuration
    are discussed in the<link
      xlink:href="http://docs.openstack.org/user-guide/content/"
      >OpenStack End User Guide</link>.</para>
  <para>Volumes do not provide concurrent access from multiple
    instances. For that you need either a traditional network
    filesystem like NFS or CIFS or a cluster filesystem such as<commit_msg>cleaned up module001-ch011-block-storage<commit_after><?xml version="1.0" encoding="utf-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
  xmlns:xi="http://www.w3.org/2001/XInclude"
  xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
  xml:id="module001-ch011-block-storage">
  <title>OpenStack Block Storage</title>
  <para><emphasis role="bold">Block Storage and OpenStack
      Compute</emphasis></para>
  <para>OpenStack provides two classes of block storage, "ephemeral"
    storage and persistent "volumes". Ephemeral storage exists only
    for the life of an instance, it will persist across reboots of the
    guest operating system but when the instance is deleted so is the
    associated storage. All instances have some ephemeral storage.
    Volumes are persistent virtualized block devices independent of
    any particular instance. Volumes may be attached to a single
    instance at a time, but may be detached or reattached to a
    different instance while retaining all data, much like a USB
    drive.</para>
  <para><guilabel>Ephemeral Storage</guilabel></para>
  <para>Ephemeral storage is associated with a single unique instance.
    Its size is defined by the flavor of the instance.</para>
  <para>Data on ephemeral storage ceases to exist when the instance it
    is associated with is terminated. Rebooting the VM or restarting
    the host server, however, will not destroy ephemeral data. In the
    typical use case an instance's root filesystem is stored on
    ephemeral storage. This is often an unpleasant surprise for people
    unfamiliar with the cloud model of computing.</para>
  <para>In addition to the ephemeral root volume all flavors except
    the smallest, m1.tiny, provide an additional ephemeral block
    device varying from 20G for the m1.small through 160G for the
    m1.xlarge by default - these sizes are configurable. This is
    presented as a raw block device with no partition table or
    filesystem. Cloud aware operating system images may discover,
    format, and mount this device. For example the cloud-init package
    included in Ubuntu's stock cloud images will format this space as
    an ext3 filesystem and mount it on /mnt. It is important to note
    this a feature of the guest operating system. OpenStack only
    provisions the raw storage.</para>
  <para><guilabel>Volume Storage</guilabel></para>
  <para>Volume storage is independent of any particular instance and
    is persistent. Volumes are user created and within quota and
    availability limits may be of any arbitrary size.</para>
  <para>When first created volumes are raw block devices with no
    partition table and no filesystem. They must be attached to an
    instance to be partitioned and/or formatted. Once this is done
    they may be used much like an external disk drive. Volumes may
    attached to only one instance at a time, but may be detached and
    reattached to either the same or different instances.</para>
  <para>It is possible to configure a volume so that it is bootable
    and provides a persistent virtual instance similar to traditional
    non-cloud based virtualization systems. In this use case the
    resulting instance may still have ephemeral storage depending on
    the flavor selected, but the root filesystem (and possibly others)
    will be on the persistent volume and thus state will be maintained
    even if the instance is shutdown. Details of this configuration
    are discussed in the<link
      xlink:href="http://docs.openstack.org/user-guide/content/"
      >OpenStack End User Guide</link>.</para>
  <para>Volumes do not provide concurrent access from multiple
    instances. For that you need either a traditional network
    filesystem like NFS or CIFS or a cluster filesystem such as
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