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Edit typos in Compute chapter of Cloud Admin Guide

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Edit Section 1.1.5 Block Storage and Compute
Fix typos and edit grammar and style
Delete duplicate sentences

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nerminamiller 2013-10-14 20:14:55 -04:00
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@ -244,64 +244,51 @@
</section>
<section xml:id="section_storage-and-openstack-compute">
<title>Block Storage and Compute</title>
<para>OpenStack provides two classes of block storage, ephemeral storage and persistent
<para>OpenStack provides two classes of block storage: ephemeral storage and persistent
volumes. Ephemeral storage exists only for the life of an instance. It persists
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>
persistent virtualized block devices independent of any particular instance. </para>
<simplesect xml:id="section_about-ephemeral-storage">
<title>Ephemeral storage</title>
<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,
does not destroy ephemeral data. In the typical use case, an instance's root
file system 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 whose size
ranges from 20 GB for m1.small to 160 GB for
m1.xlarge. You can configure these sizes. This is
presented as a raw block device with no partition
table or file system. 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 format
this space as an ext3 file system and mount it on
<filename>/mnt</filename>. It is important to
note this a feature of the guest operating system.
OpenStack only provisions the raw storage.</para>
<para>Terminating the instance associated with ephemeral storage causes the loss of
data from that ephemeral storage. Rebooting the VM or restarting the host
server, however, does not destroy ephemeral data. In a typical use case, an
instance's root file system is stored on ephemeral storage. </para>
<para>In addition to the ephemeral root volume, all flavors except the smallest,
m1.tiny, provide an additional ephemeral block device whose size ranges from 20
GB for m1.small to 160 GB for m1.xlarge. You can configure these sizes. This is
presented as a raw block device with no partition table or file system.
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
format this space as an ext3 file system and mount it on
<filename>/mnt</filename>. It is important to note this a feature of the
guest operating system. OpenStack only provisions the raw storage.</para>
</simplesect>
<simplesect xml:id="section_about-persistent-storage">
<title>Volume storage</title>
<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 n partition table and no file system. 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 file system
(and possibly others) is on the persistent volume and its state is maintained
even if the instance it shut down. Details of this configuration are discussed
in the <citetitle>OpenStack Configuration Reference</citetitle> .</para>
<para>Volumes are created by users and their size may go up to the quota and
availability limits. Upon initial creation, volumes are raw block devices
without a partition table or a file system. To partition or format volumes, you
must attach them to an instance. After you attach them to an instance, you may
use volumes much like you would an external disk drive. You may attach volumes
to one instance at a time. However, you may detach and reattach volumes to
either the same or a different instance.</para>
<para>You may configure a volume so that it is bootable and provides a persistent
virtual instance similar to traditional non-cloud-based virtualization systems.
Typically, the resulting instance may still have ephemeral storage depending on
the flavor selected, but the root file system (and possibly others) may be on
the persistent volume and its state may be maintained even if the instance is
shut down. The details of this configuration are discussed in the
<citetitle>OpenStack Configuration Reference</citetitle> .</para>
<para>Volumes do not provide concurrent access from multiple instances. For that,
you need either a traditional network file system like NFS or CIFS or a cluster
file system such as GlusterFS. These may be built within an OpenStack cluster or
provisioned outside of it, but are not features provided by the OpenStack
software.</para>
file system such as GlusterFS. These systems may be built within an OpenStack
cluster or provisioned outside of it, but OpenStack software does not provide
such features.</para>
</simplesect>
</section>
</section>