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Hallo Peter, <br>
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0"><span class="x_ContentPasted0 ContentPasted0" style="display: inline !important; background-color: rgb(255, 255, 255);">[1]
<i>[...] having a smaller inode size than the subblock size means</i></span><i> there's a big wastage on disk usage, with no performance benefit to doing so[...]
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">in short - yes 😉
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">[2]
<i>[...] 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.[...]
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">you may need to consider snapshots and directories , which all contributes to MD space</span></span></div>
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">predicting the space requirements for MD for directories is always hard, because the size of a directory is
depending on the file's name length, the users will create... <br>
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">further more, using a less than 4k inode size makes also not much sense, when taking into account, that NVMEs
and other modern block storage devices comes with a hardware block size of 4k (even though GPFS still can deal with 512 Bytes per sector)
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<span class="x_elementToProof" style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; color: rgb(0, 0, 0);"><span class="ContentPasted0">hope this helps ..
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Von:</b> gpfsug-discuss <gpfsug-discuss-bounces@gpfsug.org> im Auftrag von Peter Chase <peter.chase@metoffice.gov.uk><br>
<b>Gesendet:</b> Mittwoch, 2. August 2023 11:09<br>
<b>An:</b> gpfsug-discuss@gpfsug.org <gpfsug-discuss@gpfsug.org><br>
<b>Betreff:</b> [EXTERNAL] [gpfsug-discuss] Inode size, and system pool subblock</font>
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Good Morning, 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? I'm looking at an existing filesystem,
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Good Morning,</div>
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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?</div>
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I'm looking at an existing filesystem, the inode size is 2KiB, and the subblock is 4KiB.</div>
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It feels like I'm missing something. <span style="font-family:Arial,Helvetica,sans-serif; font-size:10pt">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="x_ContentPasted0" style="display:inline!important; color:rgb(0,0,0); background-color:rgb(255,255,255)">having
a smaller inode size than the subblock size means</span> there's a big wastage on disk usage, with no performance benefit to doing so.</span></div>
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<span style="font-family:Arial,Helvetica,sans-serif; font-size:10pt">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.</span></div>
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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!</div>
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Sincerely,</div>
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<span style="font-size:10pt; font-family:Arial,sans-serif,serif,EmojiFont; color:black"><span style="font-size:10pt; font-family:Arial,Helvetica,sans-serif; color:rgb(0,0,0)">Pete Chase</span><br>
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<p style="margin-top:0px; margin-bottom:0px"><span style="font-size:10pt; color:black"><font face="Arial, Helvetica, sans-serif">UKMO</font></span></p>
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