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Resending from the right e-mail address...<br class="">
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<div class="">Begin forwarded message:</div>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">From:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><a href="mailto:gpfsug-discuss-owner@spectrumscale.org" class="">gpfsug-discuss-owner@spectrumscale.org</a><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">Subject:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><b class="">Re: [gpfsug-discuss] Blocksize</b><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">Date:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">September 29, 2016 at 10:00:36 AM CDT<br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">To:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><a href="mailto:klb@accre.vanderbilt.edu" class="">klb@accre.vanderbilt.edu</a><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(127, 127, 127, 1.0);" class=""><b class="">From:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">"Kevin L. Buterbaugh" <<a href="mailto:klb@accre.vanderbilt.edu" class="">klb@accre.vanderbilt.edu</a>><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(127, 127, 127, 1.0);" class=""><b class="">Subject:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><b class="">Re: [gpfsug-discuss] Blocksize</b><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(127, 127, 127, 1.0);" class=""><b class="">Date:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">September 29, 2016 at 10:00:29 AM CDT<br class="">
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</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">gpfsug main discussion list <<a href="mailto:gpfsug-discuss@spectrumscale.org" class="">gpfsug-discuss@spectrumscale.org</a>><br class="">
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Hi Marc and others,
<div class=""><br class="">
</div>
<div class="">I understand … I guess I did a poor job of wording my question, so I’ll try again. The IBM recommendation for metadata block size seems to be somewhere between 256K - 1 MB, depending on who responds to the question. If I were to hypothetically
use a 256K metadata block size, does the “1/32nd of a block” come into play like it does for “not metadata”? I.e. 256 / 32 = 8K, so am I reading / writing *2* inodes (assuming 4K inode size) minimum?</div>
<div class=""><br class="">
</div>
<div class="">And here’s a really off the wall question … yesterday we were discussing the fact that there is now a single inode file. Historically, we have always used RAID 1 mirrors (first with spinning disk, as of last fall now on SSD) for metadata and
then use GPFS replication on top of that. But given that there is a single inode file is that “old way” of doing things still the right way? In other words, could we potentially be better off by using a couple of 8+2P RAID 6 LUNs?</div>
<div class=""><br class="">
</div>
<div class="">One potential downside of that would be that we would then only have two NSD servers serving up metadata, so we discussed the idea of taking each RAID 6 LUN and splitting it up into multiple logical volumes (all that done on the storage array,
of course) and then presenting those to GPFS as NSDs???</div>
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<div class="">Or have I gone from merely asking stupid questions to Trump-level craziness???? ;-)</div>
<div class=""><br class="">
</div>
<div class="">Kevin</div>
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<blockquote type="cite" class="">
<div class="">On Sep 28, 2016, at 10:23 AM, Marc A Kaplan <<a href="mailto:makaplan@us.ibm.com" class="">makaplan@us.ibm.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class=""><font size="2" face="sans-serif" class="">OKAY, I'll say it again. inodes are PACKED into a single inode file. So a 4KB inode takes 4KB, REGARDLESS of metadata blocksize. There is no wasted space.</font><br class="">
<br class="">
<font size="2" face="sans-serif" class="">(Of course if you have metadata replication = 2, then yes, double that. And yes, there overhead for indirect blocks (indices), allocation maps, etc, etc.)</font><br class="">
<font size="2" face="sans-serif" class=""><br class="">
And your choice is not just 512 or 4096. Maybe 1KB or 2KB is a good choice for your data distribution, to optimize packing of data and/or directories into inodes...</font><br class="">
<br class="">
<font size="2" face="sans-serif" class="">Hmmm... I don't know why the doc leaves out 2048, perhaps a typo...</font><br class="">
<br class="">
<font size="2" face="sans-serif" class="">mmcrfs x2K -i 2048</font><br class="">
<br class="">
<font size="2" face="sans-serif" class="">[root@n2 charts]# mmlsfs x2K -i</font><br class="">
<font size="2" face="sans-serif" class="">flag value description</font><br class="">
<font size="2" face="sans-serif" class="">------------------- ------------------------ -----------------------------------</font><br class="">
<font size="2" face="sans-serif" class=""> -i 2048 Inode size in bytes</font><br class="">
<br class="">
<font size="2" face="sans-serif" class="">Works for me!</font><br class="">
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