86 lines
5.9 KiB
HTML
86 lines
5.9 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Volume mounting and dismounting schedule timers" />
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<meta name="abstract" content="This topic provides information on how the iSeries server manages work requests to the directly attached optical library devices. It is a high-level view and does not include all program logic." />
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<meta name="description" content="This topic provides information on how the iSeries server manages work requests to the directly attached optical library devices. It is a high-level view and does not include all program logic." />
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<meta name="DC.Relation" scheme="URI" content="rzam4perfoptmedlib.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2004, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzam4schvolmmntdismnt" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Volume mounting and dismounting schedule timers</title>
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</head>
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<body id="rzam4schvolmmntdismnt"><a name="rzam4schvolmmntdismnt"><!-- --></a>
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<img src="./delta.gif" alt="Start of change" /><!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Volume mounting and dismounting schedule timers</h1>
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<div><p>This topic provides information on how the iSeries™ server manages work requests
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to the directly attached optical library devices. It is a high-level view
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and does not include all program logic. </p>
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<p>You can use the Change Device Description (CHGDEVMLB) command to change
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the queuing and scheduling logic used by the iSeries server for directly attached
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optical media libraries. </p>
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<p>Two timer values are associated with optical media libraries that affect
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the scheduling of volume mounting and pre-emptive dismounts. You can change
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both timer values by using the CHGDEVMLB command. The first timer value (UNLOADWAIT)
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is the unload wait time. This value determines how long the system waits for
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a new request for a mounted volume before removing it. The second timer value
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(MAXDEVTIME) is the maximum device wait time. This value determines how long
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a volume with active requests remains in a drive while other queued requests
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are waiting to use the drive.</p>
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<p>By using these two timer values, you can adjust the volume mount scheduling
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that is used by the optical media library to match your application’s use
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of optical volumes. </p>
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<p>You can change these timer values at any time; however, the new timer values
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will not become effective until the next time the device is varied on. </p>
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<p>System job priority and limit timers are used to schedule volume mounting.
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The maximum number of volumes that can be mounted is equal to the number of
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drives in the optical media library. Keep the following points in mind as
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you schedule volume mounting:</p>
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<ul><li>A volume can remain mounted in an optical drive for the maximum device
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wait time if work requests with the same or lower job priority for a different
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volume have been received. An exception to this is when you are initializing
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a rewritable volume or using DUPOPT; the volume remains in the drive until
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the operation is completed.</li>
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<li>Work requests for mounted volumes are serviced before requests of the
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same or lower job priority for volumes not mounted.</li>
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<li>For a multiple job environment, volumes are mounted based on the job priority
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for the work request. A work request from a job with a higher system job priority
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causes the required volume to be mounted to handle that request. The volume
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remains mounted for the maximum device wait time if work requests continue,
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dismounts after unload wait time inactivity, or is overridden by a work request
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from a job with higher system priority. If you are initializing a rewritable
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volume or using DUPOPT, the volume remains mounted until the operation is
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completed.</li>
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<li>If the work on a drive is interrupted because of a higher priority request,
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the maximum device wait time timer for the currently mounted volume is canceled.
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All future requests for that volume are queued for normal processing by priority.</li>
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<li>If the volume needed for a work request is not mounted within the system
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timeout (typically 30 minutes), the job fails due to a timeout.</li>
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</ul>
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<p><strong>Change job priority on active jobs</strong></p>
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<p> Due to the work management method used by i5/OS™ optical support, changing run priorities
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of an active optical job at the user level can result in loss of time allocation
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and, in some cases, cause jobs to time out. </p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzam4perfoptmedlib.htm" title="This topic discusses performance considerations that are specific to directly-attached optical libraries.">Performance considerations for directly-attached optical media libraries</a></div>
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</div>
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</div>
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<img src="./deltaend.gif" alt="End of change" /></body>
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</html>
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