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149 lines
8.1 KiB
XML
149 lines
8.1 KiB
XML
<?xml version='1.0' encoding='utf-8' ?>
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % BOOK_ENTITIES SYSTEM "cloudstack.ent">
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%BOOK_ENTITIES;
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]>
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<!-- Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<section id="vm-snapshots">
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<title>Virtual Machine Snapshots for VMware</title>
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<para>(VMware hosts only)
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In addition to the existing &PRODUCT; ability to snapshot individual VM volumes,
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you can now take a VM snapshot to preserve all the VM's data volumes as well as (optionally) its CPU/memory state.
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This is useful for quick restore of a VM.
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For example, you can snapshot a VM, then make changes such as software upgrades.
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If anything goes wrong, simply restore the VM to its previous state using the previously saved VM snapshot.
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</para>
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<para>The snapshot is created using the VMware native snapshot facility. The VM snapshot
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includes not only the data volumes, but optionally also whether the VM is running or
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turned off (CPU state) and the memory contents. The snapshot is stored in &PRODUCT;'s
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primary storage.</para>
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<para>VM snapshots can have a parent/child relationship.
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Each successive snapshot of the same VM is the child of the snapshot that came before it.
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Each time you take an additional snapshot of the same VM, it saves only the differences
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between the current state of the VM and the state stored in the most recent previous snapshot.
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The previous snapshot becomes a parent, and the new snapshot is its child.
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It is possible to create a long chain of these parent/child snapshots,
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which amount to a "redo" record leading from the current state of the VM back to the
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original.</para>
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<para>If you need more information about VM snapshots, check out the VMware documentation
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and the VMware Knowledge Base, especially
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<ulink url="http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&externalId=1015180">Understanding virtual machine snapshots</ulink>.</para>
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<section id="vm-snapshot-restrictions">
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<title>Limitations on VM Snapshots</title>
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<itemizedlist>
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<listitem><para>If a VM has some stored snapshots, you can't attach new volume to the VM
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or delete any existing volumes.
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If you change the volumes on the VM, it would become impossible to restore the VM snapshot
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which was created with the previous volume structure.
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If you want to attach a volume to such a VM, first delete its snapshots.
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</para></listitem>
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<listitem><para>VM snapshots which include both data volumes and memory can't be kept if you change the VM's
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service offering. Any existing VM snapshots of this type will be discarded.</para></listitem>
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<listitem>
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<para>You can't make a VM snapshot at the same time as you are taking a volume
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snapshot.</para>
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</listitem>
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<listitem>
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<para>The "quiesce" option is not supported. This option is provided by the underlying
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VMware snapshot facility so that you can choose whether to quiesce the file system
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on a running virtual machine before taking the snapshot. In &PRODUCT;, the quiesce option is always
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set to false; the file system is not quiesced before taking a snapshot of a running VM.
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</para>
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</listitem>
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<listitem><para>You should use only &PRODUCT; to create VM snapshots on VMware hosts managed by &PRODUCT;.
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Any snapshots that you make directly on vSphere will not be tracked in &PRODUCT;.</para></listitem>
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</itemizedlist>
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</section>
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<section id="vm-snapshot-configure">
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<title>Configuring VM Snapshots</title>
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<para>The cloud administrator can use global configuration variables to control the behavior of VM snapshots.
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To set these variables, go through the Global Settings area of the &PRODUCT; UI.</para>
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<informaltable>
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<tgroup cols="2" align="left" colsep="1" rowsep="1">
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<thead>
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<row>
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<entry><para>Configuration Setting Name</para></entry>
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<entry><para>Description</para></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><para>vmsnapshots.max</para></entry>
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<entry><para>The maximum number of VM snapshots that can be saved for any given virtual machine in the cloud.
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The total possible number of VM snapshots in the cloud is (number of VMs) * vmsnapshots.max.
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If the number of snapshots for any VM ever hits the maximum, the older ones are removed
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by the snapshot expunge job.
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</para></entry>
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</row>
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<row>
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<entry><para>vmsnapshot.create.wait</para></entry>
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<entry><para>Number of seconds to wait for a snapshot job to succeed before declaring failure and issuing an error.</para></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</section>
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<section id="vm-snapshot-usage">
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<title>Using VM Snapshots</title>
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<para>To create a VM snapshot using the &PRODUCT; UI:</para>
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<orderedlist>
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<listitem><para>Log in to the &PRODUCT; UI as a user or administrator.</para></listitem>
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<listitem><para>Click Instances.</para></listitem>
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<listitem><para>Click the name of the VM you want to snapshot.</para></listitem>
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<listitem><para>Click the Take VM Snapshot button.
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<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/VMSnapshotButton.png" format="PNG"/>
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</imageobject>
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</inlinemediaobject></para>
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<note><para>If a snapshot is already in progress, then clicking this button will have no effect.</para></note><para/>
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</listitem>
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<listitem><para>Provide a name and description. These will be displayed in the VM Snapshots list.</para></listitem>
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<listitem><para>(For running VMs only) If you want to include the VM's memory in the snapshot, click the
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Memory checkbox. This saves the CPU and memory state of the virtual machine. If you
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don't check this box, then only the current state of the VM disk is saved. Checking
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this box makes the snapshot take longer.</para></listitem>
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<listitem><para>Click OK.</para></listitem>
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</orderedlist>
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<para>To delete a snapshot or restore a VM to the state saved in a particular snapshot:</para>
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<orderedlist>
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<listitem><para>Navigate to the VM as described in the earlier steps.</para></listitem>
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<listitem><para>Click View VM Snapshots.</para></listitem>
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<listitem><para>In the list of snapshots, click the name of the snapshot you want to work with.</para></listitem>
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<listitem><para>Depending on what you want to do:</para>
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<para>To delete the snapshot, click the Delete button.
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<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/delete-button.png" format="PNG"/>
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</imageobject>
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</inlinemediaobject></para>
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<para>To revert to the snapshot, click the Revert button.
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<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/revert-vm.png" format="PNG"/>
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</imageobject>
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</inlinemediaobject></para>
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</listitem>
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</orderedlist>
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<note><para>VM snapshots are deleted automatically when a VM is destroyed.
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You don't have to manually delete the snapshots in this case.</para></note>
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</section>
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</section>
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