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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Peter,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"> “</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Meaning with a 4K subblock, and a 2K inode, reading the inode would return its contents and 2K of empty subblock
every time”<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I believe that a 2k inode *<b>does</b>* save space, hence more files in the filesystem for a given size of the system metadata pool.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">However with modern 4k disk block sizes, you pay the price of a performance penalty.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Hence unless space constrained, you should use 4k inodes always.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Also remember that GPFS supports Data-on-Metadata (DoM in Lustre-speak), so 4k inodes can store small files (up to c. 3k), and so save significant space in the data pools (where the subblock size
is at least 8kB and in your case probably 128kB.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="line-height:12.0pt"><b><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Daniel Kidger<br>
</span></b><span style="color:black">HPC Storage Solutions Architect, EMEA</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><br>
</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#040400"><a href="mailto:daniel.kidger@hpe.com"><span style="color:#040400">daniel.kidger@hpe.com</span></a><br>
<br>
</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">+44 (0)7818 522266 <br>
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</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#040400"><a href="http://www.hpe.com/"><b><span style="color:black;text-decoration:none">hpe.com</span></b></a><br>
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</span><img border="0" width="190" height="96" style="width:1.9791in;height:1.0in" id="Picture_x0020_1" src="cid:image001.png@01D9C540.C15BD4A0"><o:p></o:p></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> gpfsug-discuss <gpfsug-discuss-bounces@gpfsug.org>
<b>On Behalf Of </b>Peter Chase<br>
<b>Sent:</b> 02 August 2023 10:10<br>
<b>To:</b> gpfsug-discuss@gpfsug.org<br>
<b>Subject:</b> [gpfsug-discuss] Inode size, and system pool subblock<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Good Morning,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">I have a question about inode size vs subblock size. Can anyone think of a reason that the chosen inode size of a scale filesystem should be smaller than the subblock
size for the metadata pool?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">I'm looking at an existing filesystem, the inode size is 2KiB, and the subblock is 4KiB.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">It feels like I'm missing something. If I've understood the docs on blocks and subblocks correctly, it sounds like the subblock is the smallest atomic access size.
Meaning with a 4K subblock, and a 2K inode, reading the inode would return its contents and 2K of empty subblock every time. So, in my head (and maybe only there), <span class="contentpasted0"><span style="background:white">having a smaller inode size than
the subblock size means</span></span> there's a big wastage on disk usage, with no performance benefit to doing so.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">I believe I'm correct in saying that inodes are not the only things to live on the metadata pool, so I assume that some other metadata might benefit from the larger
block/subblock size. But looking at the number of inodes, the inode size, and the space consumed in the system pool, it really looks like the majority of space consumed is by inodes.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">As I said, I feel like I'm missing something, so if anyone can tell me where I'm wrong it would be greatly appreciated!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Sincerely,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">Pete Chase</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">UKMO</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
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