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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;">The software I use is RedHat Virtualization. When using Posix compatible FS, it seems to perform direct I / O with a block size of 256512 bytes.</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;">If I can't resolve the issue with my storage configuration, I will contact RedHat.</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;">Your answer was very helpful.</p>
<p style="margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;color:rgb(0, 0, 0);line-height:1.2;">Thank you.</p>
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<p style="color:rgb(0, 0, 0);margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;line-height:1.2;">보내는사람 : Andreas Dilger <adilger@whamcloud.com></p>
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<p style="color:rgb(0, 0, 0);margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;line-height:1.2;">받는사람 : 김형근 <okok102928@fusiondata.co.kr></p>
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<p style="color:rgb(0, 0, 0);margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;line-height:1.2;">참조 : lustre-discuss@lists.lustre.org <lustre-discuss@lists.lustre.org></p>
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<p style="color:rgb(0, 0, 0);margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;line-height:1.2;">보낸 날짜 : 2018-10-25 16:47:58</p>
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<p style="color:rgb(0, 0, 0);margin-top:0px;margin-bottom:0px;font-family:굴림체;font-size:9pt;line-height:1.2;">제목 : Re: [lustre-discuss] dd oflag=direct error (512 byte Direct I/O)</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;">On Oct 25, 2018, at 15:05, 김형근 </p>
<okok102928 fusiondata.co.kr="">
wrote:
<br /> >
<br /> > Hi.
<br /> > It's a pleasure to meet you, the lustre specialists.
<br /> > (I do not speak English well ... Thank you for your understanding!)
<br />
<br /> Your english is better than my Korean. :-)
<br />
<br /> > I used the dd command in lustre mount point. (using the oflag = direct option)
<br /> >
<br /> > ------------------------------------------------------------
<br /> > dd if = / dev / zero of = / mnt / testfile oflag = direct bs = 512 count = 1
<br /> > ------------------------------------------------------------
<br /> >
<br /> > I need direct I / O with 512 byte block size.
<br /> > This is a required check function on the software I use.
<br />
<br /> What software is it? Is it possible to change the application to use
<br /> 4096-byte alignment?
<br />
<br /> > But unfortunately, If the direct option is present,
<br /> > bs must be a multiple of 4K (4096) (for 8K, 12K, 256K, 1M, 8M, etc.) for operation.
<br /> > For example, if you enter a value such as 512 or 4095, it will not work. The error message is as follows.
<br /> >
<br /> > 'error message: dd: error writing [filename]: invalid argument'
<br /> >
<br /> > My test system is all up to date. (RHEL, lustre-server, client)
<br /> > I have used both ldiskfs and zfs for backfile systems. The result is same.
<br /> >
<br /> >
<br /> > My question is simply two.
<br /> >
<br /> > 1. Why does DirectIO work only in 4k multiples block size?
<br />
<br /> The client PAGE_SIZE on an x86 system is 4096 bytes. The Lustre client
<br /> cannot cache data smaller than PAGE_SIZE, so the current implementation
<br /> is limited to have O_DIRECT read/write being a multiple of PAGE_SIZE.
<br />
<br /> I think the same would happen if you try to use O_DIRECT on a disk with
<br /> 4096-byte native sector drive (https://en.wikipedia.org/w/index.php?title=Advanced_Format§ion=5#4K_native )?
<br />
<br /> > 2. Can I change the settings of the server and client to enable 512bytes of DirectIO?
<br />
<br /> This would not be possible without changing the Lustre client code.
<br /> I don't know how easily this is possible to do and still ensure that
<br /> the 512-byte writes are handled correctly.
<br />
<br /> So far we have not had other requests to change this limitation, so
<br /> it is not a high priority to change on our side, especially since
<br /> applications will have to deal with 4096-byte sectors in any case.
<br />
<br /> Cheers, Andreas
<br /> ---
<br /> Andreas Dilger
<br /> Principal Lustre Architect
<br /> Whamcloud
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</okok102928>
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