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130 lines
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<meta name="abstract" content="Journaling affects the disk arms that store the journal receiver." />
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<title>Frequently asked questions about journaling and disk arm usage</title>
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<body id="rzakidiskarm"><a name="rzakidiskarm"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Frequently asked questions about journaling and disk arm usage</h1>
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<div><p>Journaling affects the disk arms that store the journal receiver.</p>
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<p>How the journal receiver affects the disk arm depend on several factors:</p>
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<ul><li>The threshold setting you are using for your journal receiver.</li>
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<li>Whether or not you are using a maximum receiver-size option.</li>
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<li>The way in which the system writes journal entries to disk.</li>
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</ul>
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<p id="rzakidiskarm__top"><a name="rzakidiskarm__top"><!-- --></a>The following are frequently asked questions about journaling
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and disk arm usage:</p>
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<p><a href="#rzakidiskarm__howmany">How many arms in my disk unit will journaling use?</a></p>
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<p><a href="#rzakidiskarm__whichparms">Which journal parameters and settings affect the number of the disk arms the journal receiver uses?</a></p>
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<p><a href="#rzakidiskarm__newarms">Why is the system not using the new disk arms I added to my disk pool?</a></p>
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<p><a href="#rzakidiskarm__diskarms">Why are some disk arms used by journal receivers noticeably busier than the others and what can I do to spread out the usage?</a></p>
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<div class="section" id="rzakidiskarm__howmany"><a name="rzakidiskarm__howmany"><!-- --></a><h4 class="sectiontitle">How many arms in my disk unit will journaling
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use?</h4><p>How many disk arms the journal receiver uses depends on your
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threshold value and whether you use a maximum receiver-size option. When you
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create a journal receiver and attach it to a journal that does not specify
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a maximum receiver-size option, the system spreads the journal receiver on
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up to 10 disk arms. If you use a maximum receiver-size option, the system
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spreads the journal receiver on up to 100 disk arms. Some rules that the system
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uses when determining the number of disk arms are as follows:</p>
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<ul><li>The system cannot use more disk arms than are available in your disk pool.</li>
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<li>The system will not use fewer than 10 disk arms if that many arms are
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available.</li>
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</ul>
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<p>You can use the following formula to determine how many disk arms
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you will use:</p>
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<p><samp class="codeph">Number of disk arms = Journal receiving threshold
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setting / 64 MB</samp></p>
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<p>For more information about disk arm use and
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journaling see <a href="http://www.redbooks.ibm.com/abstracts/sg246286.html?Open" target="_blank">Striving for Optimal Journal Performance on DB2<sup>®</sup> Universal
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Database for iSeries™</a>.</p>
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<p><strong><a href="rzakidiskarm.htm#rzakidiskarm__top">Back to questions</a></strong></p>
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</div>
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<div class="section" id="rzakidiskarm__whichparms"><a name="rzakidiskarm__whichparms"><!-- --></a><h4 class="sectiontitle">Which journal parameters and settings affect
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the number of the disk arms the journal receiver uses?</h4><p>The threshold
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for the journal receiver and whether you use a maximum receiver-size option
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have the largest effect on how many disk arms the journal receiver uses. If
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you have a system which is before V5R2, removing internal entries also affects
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the number of disk arms that are used.</p>
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<p><strong><a href="rzakidiskarm.htm#rzakidiskarm__top">Back
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to questions</a></strong></p>
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</div>
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<div class="section" id="rzakidiskarm__newarms"><a name="rzakidiskarm__newarms"><!-- --></a><h4 class="sectiontitle">Why is the system not using the new disk arms
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I added to my disk pool?</h4><p>There can be a several reasons. First,
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to use the newly added disk arms, you must perform a change journal operation
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to attach a new journal receiver. Also, the system does not necessarily use
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all of the disk arms in a disk pool. If you are not using a maximum receiver-size
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option, the most disk arms the system will spread the receiver over is ten.
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The number of disk arms the receiver uses also depends on the threshold you
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use for your journal receiver. If you use a maximum receiver-size option and
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increase your threshold, it is more likely that your new disk arm will be
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used.</p>
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<p>If you use system-managed access-path protection (SMAPP), the
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system generates internal journal entries to protect the access paths for
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database files. If you have not upgraded to at least V5R2, setting your journal
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receiver to remove internal entries is an issue if you are not producing these
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internal entries. Before V5R2, removing internal entries can steal disk arms
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from the normal journal entries. For example, if you have six disk arms in
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the disk pool housing your journal receiver and remove internal entries, two
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arms are dedicated to the internal entries and four arms are used for your
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regular journal entries. If you do not produce any internal entries, those
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two arms remained idle. For V5R2 and later, this is not an issue.</p>
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<p>For
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more information about disk arm use and journaling see <a href="http://www.redbooks.ibm.com/abstracts/sg246286.html?Open" target="_blank">Striving
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for Optimal Journal Performance on DB2 Universal Database for iSeries</a>.</p>
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<p id="rzakidiskarm__busy"><a name="rzakidiskarm__busy"><!-- --></a><strong><a href="rzakidiskarm.htm#rzakidiskarm__top">Back to questions</a></strong></p>
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</div>
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<div class="section" id="rzakidiskarm__diskarms"><a name="rzakidiskarm__diskarms"><!-- --></a><h4 class="sectiontitle">Why are some disk arms used by journal receivers
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noticeably busier than the others and what can I do to spread out the usage?</h4><p>The
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journal receivers probably use some disk arms more than other because of the
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way journal management writes journal entries to disk. When the system produces
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journal entries, journal management stores the journal entries in memory.
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When it is ready, journal management sends the journal entries to a disk arm
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in one group. When the next group of journal entries are ready, journal management
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sends the entries to the next disk arm. Journal management continues in this
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sequential manner until all of the disk arms it uses have received a group
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of journal entries. The cycle then repeats.</p>
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<p>You can spread out the usage
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by increasing your threshold and using a maximum receiver-size option.</p>
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<p>For
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more information about disk arm use and journaling see <a href="http://www.redbooks.ibm.com/abstracts/sg246286.html?Open" target="_blank">Striving
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for Optimal Journal Performance on DB2 Universal Database for iSeries</a>.</p>
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<p><strong><a href="rzakidiskarm.htm#rzakidiskarm__top">Back to questions</a></strong></p>
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</div>
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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="rzakiplnuseaux.htm" title="If you are journaling an object, journal management writes a copy of every object change to the journal receiver. It writes additional entries for object level activity, such as opening and closing the object, adding a member, or changing an object attribute. If you have a busy system and journal many objects, your journal receivers can quickly become very large.">Plan for journal use of auxiliary storage</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzakijrnsysperform.htm" title="Journal management prevents transactions from being lost if your system ends abnormally or has to be recovered. To do this, journal management writes changes to journaled objects immediately to the journal receiver in auxiliary storage. This increases the disk activity on your system and can have a noticeable affect on system performance. Journaling also increases the overhead associated with opening objects and closing objects.">Journal management and system performance</a></div>
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<div><a href="rzakithreshold.htm" title="When you create a journal receiver with iSeries Navigator or the Create Journal Receiver (CRTJRNRCV) command, you specify a disk space threshold that indicates when you want the system to warn you or take action.">Threshold (disk space) for journal receivers</a></div>
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<div><a href="rzakisizeoptions.htm" title="A journal receiver holds journal entries that you might use for recovery and entries that the system might use for recovery. For example, you might use record level entries, such as database record changes, and file level entries, such as the entry for opening or closing a file. Also, the system writes entries that you never see or use, such as entries for explicitly journaled access paths, for SMAPP, or for commitment control.">Receiver size options for journals</a></div>
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</div>
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</div>
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</body>
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</html>
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