<div dir="ltr">Ah. that's a good point about the snapshots.</div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Mar 17, 2015 at 12:01 PM, Sanchez, Paul <span dir="ltr"><<a href="mailto:Paul.Sanchez@deshaw.com" target="_blank">Paul.Sanchez@deshaw.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">It\u2019s also required for per-fileset snapshots, which are useful if you have differing snapshot requirements or want the ability to flush high-churn snapshots
that are consuming an unexpected amount of space, but with better resolution than a whole filesystem.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">-Paul Sanchez<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> <a href="mailto:gpfsug-discuss-bounces@gpfsug.org" target="_blank">gpfsug-discuss-bounces@gpfsug.org</a> [mailto:<a href="mailto:gpfsug-discuss-bounces@gpfsug.org" target="_blank">gpfsug-discuss-bounces@gpfsug.org</a>]
<b>On Behalf Of </b>Zachary Giles<br>
<b>Sent:</b> Tuesday, March 17, 2015 11:49 AM<br>
<b>To:</b> gpfsug main discussion list<br>
<b>Subject:</b> Re: [gpfsug-discuss] Fragmented Inode Space and Performance of Policy Scans<u></u><u></u></span></p><div><div class="h5">
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">I've always wondered also what the decision point is to make new inode tables per fileset. <u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Sounds like the main benefit is scope of mmapplypolicy ( and other commands maybe ) and subblocks being grouped together for performance reasons. Is that right?<u></u><u></u></p>
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<p class="MsoNormal">Are there other benefits like portability or grouping a fileset's inode table into specific failure groups (in the system pool) etc?<u></u><u></u></p>
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<p class="MsoNormal">Any downsides? ( for example: now you have more overall metadata reads.. or only a limited number of inode tables.. or total number of inodes in the system is higher due to overallocation on N tables ? )<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">-Zach<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Tue, Mar 17, 2015 at 10:22 AM, Marc A Kaplan <<a href="mailto:makaplan@us.ibm.com" target="_blank">makaplan@us.ibm.com</a>> wrote:<u></u><u></u></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Arial","sans-serif"">Luke,
</span><br>
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<span style="font-family:"Arial","sans-serif""> Thanks for your question. Independent filesets and their inodes are not implemented the way you might be imagining or guessing.</span>
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<span style="font-family:"Arial","sans-serif"">Suppose you have two independent filesets "root" and "fset2" in the same GPFS file system.</span>
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<span style="font-family:"Arial","sans-serif"">It is true that all the inode records (typically 512 bytes each - see mmcrfs) go into the same special file. BUT if you look at any given metadata allocation block --metadata-block-size (defaults to 256K) you'll
only see inodes for either "root" or "fset2" not both in the same block.</span> <br>
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<span style="font-family:"Arial","sans-serif"">Moreover we try to "pre"-allocate several blocks of inodes for the same independent fileset contiguously - so that typically GPFS can do one seek and then read several blocks of inodes from the same independent
fileset.</span> <br>
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<span style="font-family:"Arial","sans-serif"">So there can be performance advantages to using independent filesets and restricting your mmapplypolicy scans to just the fileset you need.</span>
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<span style="font-family:"Arial","sans-serif"">To gain maximal advantage, use the following form of the command:</span>
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<span style="font-family:"Arial","sans-serif""> mmapplypolicy /gpfs/path-to-the-directory-tree-I-want-to-scan --scope {fileset | inodespace } ...</span>
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<span style="font-family:"Arial","sans-serif""> </span><br>
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<span style="font-family:"Arial","sans-serif"">An inodespace is the set of all inodes in an independent fileset. An inodespace may contain several "dependent" filesets. </span>
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<span style="font-family:"Arial","sans-serif""><br>
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<u></u><img src="cid:image001.gif@01D060A9.415DA4E0" align="left" alt="Marc A Kaplan"><u></u><br>
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<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">-- <u></u><u></u></p>
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<p class="MsoNormal">Zach Giles<br>
<a href="mailto:zgiles@gmail.com" target="_blank">zgiles@gmail.com</a><u></u><u></u></p>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature">Zach Giles<br><a href="mailto:zgiles@gmail.com">zgiles@gmail.com</a></div>
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