<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><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></div></div></blockquote><div><br></div><div>Since they are already HDDs, this feature won't apply because it makes no sense for them.</div><div><br></div><div>For SSDs, cloud users prefer to spread them across multiple servers to fully utilize disk bandwidth. Bandwidth is likely the first priority. Once that's solved, they want larger capacity so they don't have to load new worksets each time. </div><div><br></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>
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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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