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Docs. CLOUDSTACK-304. New section: snapshot-throttling.xml. In working-with-snapshots.xml: include the new section.

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Jessica Tomechak 2013-01-30 16:17:44 -08:00
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<?xml version='1.0' encoding='utf-8' ?>
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "file:///C:/Program%20Files%20(x86)/Publican/DocBook_DTD/docbookx.dtd" [
<!ENTITY % BOOK_ENTITIES SYSTEM "cloudstack.ent">
%BOOK_ENTITIES;
]>
<section id="snapshot-throttling">
<title>Snapshot Job Throttling</title>
<para>When a snapshot of a virtual machine is requested, the snapshot job runs on the same
host where the VM is running or, in the case of a stopped VM, the host where it ran last. If
many snapshots are requested for VMs on a single host, this can lead to problems with too
many snapshot jobs overwhelming the resources of the host.</para>
<para>To address this situation, the cloud's root administrator can throttle how many snapshot
jobs are executed simultaneously on the hosts in the cloud by using the global configuration
setting concurrent.snapshots.threshold.perhost. By using this setting, the administrator can
better ensure that snapshot jobs do not time out and hypervisor hosts do not experience
performance issues due to hosts being overloaded with too many snapshot requests.</para>
<para>Set concurrent.snapshots.threshold.perhost to a value that represents a best guess about
how many snapshot jobs the hypervisor hosts can execute at one time, given the current
resources of the hosts and the number of VMs running on the hosts. If a given host has more
snapshot requests, the additional requests are placed in a waiting queue. No new snapshot
jobs will start until the number of currently executing snapshot jobs falls below the
configured limit.</para>
<para>The admin can also set job.expire.minutes to place a maximum on how long a snapshot
request will wait in the queue. If this limit is reached, the snapshot request fails and
returns an error message. </para>
</section>

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docs/en-US/working-with-snapshots.xml
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<para>Snapshots may be taken for volumes, including both root and data disks. The administrator places a limit on the number of stored snapshots per user. Users can create new volumes from the snapshot for recovery of particular files and they can create templates from snapshots to boot from a restored disk.</para>
<para>Users can create snapshots manually or by setting up automatic recurring snapshot policies. Users can also create disk volumes from snapshots, which may be attached to a VM like any other disk volume. Snapshots of both root disks and data disks are supported. However, &PRODUCT; does not currently support booting a VM from a recovered root disk. A disk recovered from snapshot of a root disk is treated as a regular data disk; the data on recovered disk can be accessed by attaching the disk to a VM.</para>
<para>A completed snapshot is copied from primary storage to secondary storage, where it is stored until deleted or purged by newer snapshot.</para>
<xi:include href="snapshot-throttling.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
</section>