f125a8b892
This change addresses a long-standing issue in rST documentation imported from XML.
That import process added backslash escapes in front of various characters. The three
most common being '(', ')', and '_'.
These instances are removed.
Signed-off-by: Ron Stone <ronald.stone@windriver.com>
Change-Id: Id43a9337ffcd505ccbdf072d7b29afdb5d2c997e
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79 lines
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.. ugv1564682723675
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.. _nova-ephemeral-storage:
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======================
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Nova Ephemeral Storage
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======================
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.. contents::
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:local:
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:depth: 1
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This is the default OpenStack storage option used for creating VMs. Virtual
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machine instances are typically created with at least one ephemeral disk which
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is used to run the VM guest operating system and boot partition.
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Ephemeral storage for VMs, which includes swap disk storage, ephemeral disk
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storage, and root disk storage if the VM is configured for boot-from-image, is
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implemented by the **nova** service. For flexibility and scalability, this
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storage is defined using a **nova-local** local volume group created on the
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compute hosts.
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The nova-local group can be backed locally by one or more disks or partitions
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on the compute host, or remotely by resources on the internal Ceph cluster (on
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controller or storage hosts). If it is backed locally on the compute host,
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then it uses CoW-image storage backing. For more information about
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**nova-local** backing options, see |stor-doc|:
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:ref:`Block Storage for Virtual Machines <block-storage-for-virtual-machines>`.
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Compute hosts are grouped into host aggregates based on whether they offer CoW
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or remote Ceph-backed local storage. The host aggregates are used for
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instantiation scheduling.
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.. _nova-ephemeral-storage-section-N10149-N1001F-N10001:
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------------
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Instances LV
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------------
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For storage on compute hosts, CoW-image backing uses an instances logical
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volume, or **Instances LV**. This contains the /etc/nova/instances file system,
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and is used for the following:
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.. _nova-ephemeral-storage-ul-mrd-bxv-q5:
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- the nova image cache, containing images downloaded from Glance
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- various small nova control and log files, such as the libvirt.xml file,
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which is used to pass parameters to **libvirt** at launch, and the console.log
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file
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For CoW-image-backed local storage, **Instances LV** is also used to hold
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CoW-image disk files for use as VM disk storage. It is the only volume in
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**nova-local**.
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By default, no size is specified for the **Instances LV**. For non-root disks,
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the minimum required space is 2 GB for a **nova-local** volume group with a
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total size less that 80 GB, and 5 GB for a **nova-local** volume group larger
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or equal than 80 GB; you must specify at least this amount. You can allocate
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more **Instances LV** space to support the anticipated number of
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boot-from-image VMs, up to 50% of the maximum available storage of the local
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volume group. At least 50% free space in the volume group is required to
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provide space for allocating logical volume disks for launched instances. The
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value provided for the **Instance LV Size** is limited by this maximum.
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Instructions for allocating the **Instances LV Size** using the Web
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administration interface or the CLI are included in as part of configuring the
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compute nodes. Suggested sizes are indicated in the Web administration
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interface.
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.. caution::
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If less than the minimum required space is available, the compute host
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cannot be unlocked.
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