<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, Nov 4, 2025 at 8:37 AM Andreas Dilger <<a href="mailto:adilger@ddn.com">adilger@ddn.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">



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On Nov 3, 2025, at 18:58, Oleg Drokin via lustre-devel <<a href="mailto:lustre-devel@lists.lustre.org" target="_blank">lustre-devel@lists.lustre.org</a>> wrote:<br>
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<div><span style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;display:inline">On
 Mon, 2025-11-03 at 16:33 -0800, Jinshan Xiong wrote:</span><br style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none">
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I guess users won't have 1PB OSTs, will they?<br>
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<span style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;display:inline">There
 probably are already? NASA has a known 0.5P OST configuration:</span><br style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none">
<a href="https://www.nas.nasa.gov/hecc/support/kb/lustre-progressive-file-layout-(pfl)-with-ssd-and-hdd-pools_680.html#:~:text=The%20available%20SSD%20space%20in%20each%20filesystem,decimal%20(far%20right)%20labels%20of%20each%20OST" style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" target="_blank">https://www.nas.nasa.gov/hecc/support/kb/lustre-progressive-file-layout-(pfl)-with-ssd-and-hdd-pools_680.html#:~:text=The%20available%20SSD%20space%20in%20each%20filesystem,decimal%20(far%20right)%20labels%20of%20each%20OST</a></div></blockquote></div></div></blockquote><div><br></div><div>In that case, they don't need to use this feature.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div><blockquote type="cite"><div><br style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none">
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In order to maximize rebuild performance for declustered parity RAID,
<div>there are OSTs in production with 90x20TB HDDs = 1.4 PB today,</div>
<div>and requests to have even larger OSTs.  We've done a bunch of work</div>
<div>to improve huge ldiskfs OST performance, including the hybrid OST</div>
<div>patches like <a href="https://review.whamcloud.com/51625" target="_blank">https://review.whamcloud.com/51625</a> ("LU-16750 ldiskfs:</div>
<div>optimize metadata allocation for hybrid LUNs"), but there could still</div>
<div>be further improvements in supporting such large OSTs.<br>
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<div>Cheers, Andreas</div>
<div>—</div>
<div>Andreas Dilger</div>
<div>Lustre Principal Architect</div>
<div>Whamcloud/DDN</div>
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