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46 lines
2.7 KiB
XML
46 lines
2.7 KiB
XML
<?xml version='1.0' encoding='utf-8' ?>
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<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "file:///C:/Program%20Files%20(x86)/Publican/DocBook_DTD/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="snapshot-throttling">
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<title>Snapshot Job Throttling</title>
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<para>When a snapshot of a virtual machine is requested, the snapshot job runs on the same
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host where the VM is running or, in the case of a stopped VM, the host where it ran last. If
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many snapshots are requested for VMs on a single host, this can lead to problems with too
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many snapshot jobs overwhelming the resources of the host.</para>
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<para>To address this situation, the cloud's root administrator can throttle how many snapshot
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jobs are executed simultaneously on the hosts in the cloud by using the global configuration
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setting concurrent.snapshots.threshold.perhost. By using this setting, the administrator can
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better ensure that snapshot jobs do not time out and hypervisor hosts do not experience
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performance issues due to hosts being overloaded with too many snapshot requests.</para>
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<para>Set concurrent.snapshots.threshold.perhost to a value that represents a best guess about
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how many snapshot jobs the hypervisor hosts can execute at one time, given the current
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resources of the hosts and the number of VMs running on the hosts. If a given host has more
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snapshot requests, the additional requests are placed in a waiting queue. No new snapshot
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jobs will start until the number of currently executing snapshot jobs falls below the
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configured limit.</para>
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<para>The admin can also set job.expire.minutes to place a maximum on how long a snapshot
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request will wait in the queue. If this limit is reached, the snapshot request fails and
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returns an error message. </para>
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</section>
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