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<div>Hello,</div>
<div><br>
</div>
<div>The direct writes are problematic on both writes and rewrites. Rewrites alone are another issue we have noticed.</div>
<div>Since indirect (direct=0) workloads are fine, it seems that the easiest solution could be to force indirect IO operations for all workloads. However we didn't find such possibility.<br>
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<div><span>
<pre>-- <br></pre>
<div style="font-size: 9pt; color: rgb(89, 89, 89); font-family: verdana;">S přáním pěkného dne / Best regards</div>
<br style="caret-color: rgb(46, 52, 54); color: rgb(46, 52, 54);">
<div style="font-size: 11pt; color: rgb(220, 38, 30); font-family: verdana;"><b>Mgr. Peter Hruška</b><br>
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<div>On Tue, 2024-03-12 at 09:59 +0100, Zdenek Salvet wrote:</div>
<blockquote type="cite" style="margin:0 0 0 .8ex; border-left:2px #729fcf solid;padding-left:1ex">
<div>EXTERNÍ ODESÍLATEL<br>
</div>
<div><br>
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<div><br>
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<div>On Mon, Mar 11, 2024 at 01:21:32PM +0000, Peter Hruška wrote:<br>
</div>
<blockquote type="cite" style="margin:0 0 0 .8ex; border-left:2px #729fcf solid;padding-left:1ex">
<div>We encountered a problem with performance of writes on GPFS when the application uses direct io access. To simulate the issue it is enough to run fio with option direct=1. The performance drop is quite dramatic - 250 MiB/s vs. 2955 MiB/s. We've tried to
instruct GPFS to ignore direct IO by using "disableDIO=yes". The directive didn't have any effect. Is there any possibility how to achieve that GPFS would ignore direct IO requests and use caching for everything?<br>
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<div><br>
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<div>Hello,<br>
</div>
<div>did you use pre-allocated file(s) (was it re-write) ?<br>
</div>
<div>libaio traffic is not really asynchronous with respect to necessary metadata<br>
</div>
<div>operations (allocating new space and writing allocation structures to disk)<br>
</div>
<div>in most Linux filesystems and I guess this case is not heavily optimized<br>
</div>
<div>in GPFS either (dioSmallSeqWriteBatching feature may help a little but<br>
</div>
<div>it targets different scenario I think).<br>
</div>
<div><br>
</div>
<div>Best regards,<br>
</div>
<div>Zdenek Salvet <a href="mailto:salvet@ics.muni.cz">
salvet@ics.muni.cz</a><br>
</div>
<div>Institute of Computer Science of Masaryk University, Brno, Czech Republic<br>
</div>
<div>and CESNET, z.s.p.o., Prague, Czech Republic<br>
</div>
<div>Phone: ++420-549 49 6534 Fax: ++420-541 212 747<br>
</div>
<div>----------------------------------------------------------------------------<br>
</div>
<div> Teamwork is essential -- it allows you to blame someone else.<br>
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