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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">Hi.</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">It's a pleasure to meet you, the lustre specialists.</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">(I do not speak English well ... Thank you for your understanding!)</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">I used the dd command in lustre mount point. (using the oflag = direct option)</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">dd if = / dev / zero of = / mnt / testfile oflag = direct bs = 512 count = 1</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">I need direct I / O with 512 byte block size.</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">This is a required check function on the software I use.</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">But unfortunately, If the direct option is present,</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">bs must be a multiple of 4K (4096) (for 8K, 12K, 256K, 1M, 8M, etc.) for operation.</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">For example, if you enter a value such as 512 or 4095, it will not work. The error message is as follows.</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">'error message: dd: error writing [filename]: invalid argument'</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">My test system is all up to date. (RHEL, lustre-server, client)</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">I have used both ldiskfs and zfs for backfile systems. The result is same.</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">My question is simply two.</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">1. Why does DirectIO work only in 4k multiples block size?</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">2. Can I change the settings of the server and client to enable 512bytes of DirectIO?</p>
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<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">I wait for your answer. Thank you.</p>
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